And, in case that’s hard to remember, for short we will refer to it as “so-lo-mo,” like do-re-mi from the “Sound of Music,” except without much “Glee” for retailers.

That’s because other than the recession, this past year may represent the biggest challenge for the retail industry since the mid-’90s, when e-commerce was born.

Here’s how this daunting, yet exciting and opportunistic, trifecta played out this year:

Mobile: There’s definitely an app for that. As smartphones go mainstream, savvy shoppers use apps to price-check and read reviews of products in the store.

Result: Retailers watch in horror as shoppers leave their stores empty-handed and drive across town to another store or go online to order a different or cheaper product.

Social: Friends and social circles influence purchase decisions through the rise of Facebook and Twitter. Users check in on apps, such as Foursquare and shopkick, for discounts and incentives.

Result: Retailers who don’t bone up on their social media skills may miss out on generating conversations across the Web that result in online sales or traffic to their stores.

Local: Advertising begins shifting to Groupon and LivingSocial, as group discounting and daily deals gain popularity.

Result: At least initially, these deals have been successful at locking in sales for local stores and restaurants looking for a bump in visitors.

These trends led Cathy Halligan to leave her cushy job as chief marketing officer of Wal-Mart Stores, the world’s biggest retailer, for PowerReviews, an obscure social commerce early-stage start-up.

As the company’s SVP of marketing and sales, she explains her decision:

“I’ve been in retail for 22 years, and starting in fourth quarter of last year, I saw that consumers were adopting different tools, techniques and shopping methodologies at scale. I saw things like Groupon and Foursquare, and then there were things like [eBay's] RedLaser, which lets you scan an item on a retailer’s shelf to get a price from the retailer across the street.”

That’s a catastrophic change she hasn’t seen since her days at Blue Nile when the high-end jewelry e-retailer was just getting off the ground.

The big difference with these trends in 2010 vs. e-commerce in the mid-90s, she said, is adoption: “Consumers are adopting stuff and actually using it.”

The uptick in behavior started occurring as early as the first quarter.

Now, at the San Francisco-based company, she’s mostly focused on the social component of the retail experience.

The PowerReviews platform works across more than a thousand e-commerce sites, including REI’s, and Diapers.com (now owned by Amazon), to let consumers leave messages about products and link their reviews to their Facebook profile, if they choose.

In 2010, Facebook shifted the shopping scene to become one of the leading ways people discovered new products, she said.

The social network did so by becoming a significant source of referral traffic to e-commerce sites–and, in some cases, surpassing Google. The “Like” button allowed users to connect to brands and helped them spread virally.

The most stunning example of the year, in her opinion, was when Apple released the Beatles on iTunes and more referrals came from Facebook than from Google.

Eva Manolis, Amazon’s VP of retail customer experience, had a contrarian viewpoint for the online behemoth.

“There’s still a ton to be done. Social hasn’t really gotten farther than sending an email,” she said.

Amazon allows users to log in to their Facebook account on the site in order to get recommendations for bands, movies, etc., based on what their friends have “Liked,” but she says one of the more exciting social uses is the Wish List functionality that allows users to tag products from all over the Web to a list.

The feature is 11 years old, but it was particular popular during the 2010 holiday season, with Wish List purchases increasing six times compared to the rest of the year. Manolis said it’s logical that “the rise in being more comfortable with social is making Wish List more popular.”

But if it’s not social, it’s mobile that’s creating retail disruption this year.

EBay is not the only major retailer that has a price-comparison app. Among many barcode readers, Google has one. And this year, Amazon launched Price Check on the iPhone, which allows users to search by scanning a barcode, clicking a picture of a product or speaking the product’s name into the phone.

This week, Amazon disclosed that there were millions of Price Checks from Black Friday through its Free Super-Saver Shipping cutoff date for delivery before Christmas.

Mobile also often intersects with social.

Take shopkick, the Menlo Park, Calif.-based start-up that already counts big retailers as its clients, including Target, Macy’s, Best Buy and others.

CEO Cyriac Roeding, a former EVP for CBS’s mobile unit, created the concept to get people inside stores by giving points and other rewards to consumers who check in on their mobile phones.

Founded in the summer of 2009, shopkick is already getting some positive feedback. Sports Authority details its experiences after running several tests over a four-month period. After increasing the amount of rewards they gave, the sporting-goods store saw a 50 to 70 percent increase in shoppers walking into the store.

Users can then exchange the “kickbucks” for gift cards, Facebook Credits and more, or retailers can provide discounts on items in the store.

Likewise, Foursquare also tries to encourage consumer loyalty.

Merchants may team up with the so-lo-mo network to offer discounts or other incentives for check-ins, or for those who visit often enough to become the “Mayor.” While discounts and incentives were only beginning to take off at the start of the year, Foursquare now has a steady stream.

Just take the middle of nowhere as an example: The Pizza Hut in El Dorado, Kan., will award the Foursquare Mayor one free order of breadsticks per day with purchase of a large pizza. And in neighboring Wichita, Payless ShoeSource is giving first-time check-ins $5 off any $25 purchase.

According to Buzzillions.com reviews, the Canon (CAJ) G9 Powershot camera is ranked No. 3 in its product category.

But reviews don’t always identify their authors’ true motives. One item might be reviewed by a satisfied customer who bought the product, or it could be from someone who designed the product and wants to see it succeed. A review could even be from a manufacturer’s disgruntled employee who wants to see the product fail. Blogs can perpetuate such biased behavior by inviting people to submit reviews without verifying whether or not the members ever used the product.

This week, I tested Buzzillions.com, a free Web site owned by San Francisco-based PowerReviews Inc. that mainly posts reviews from people who have verifiably purchased the product they are appraising, according to retailers’ records. It also organizes reviews in specific categories, allowing users to search according to how they categorize themselves.

For example, someone shopping for sheets can label herself a budget, midrange or high-end shopper. A guy looking for a videogame console could call himself a gaming novice, casual gamer, frequent player or hard-core gamer. And someone on the hunt for the right shampoo could call herself a minimalist, beauty conscious or a product junkie. Selecting one of these profile labels whittles reviews down to only those best suited for the personality of the person buying the product — or perhaps receiving it as a gift.

The secret sauce behind Buzzillions is generated by surveys that over 300 retailers send to consumers. A few weeks after buying a product, consumers receive an email survey with a link to a Buzzillions questionnaire. These surveys ask consumers what they consider to be a product’s pros, cons and best uses, and its ranking according to the site’s best-out-of-five star rating system. And, following the Buzzillions formula, it asks these verified buyers to categorize themselves. Both verified users and unverified users, alike, can write reviews for the site, though verified users’ reviews are more heavily considered in the “Buzzillions Rank” system.

The “Buzzillions Rank” shows a product’s standing in its particular category, based on an algorithm applied to the survey data. This formulated ranking is based on three things: a product’s star rating; the number of reviews it receives; and the reliability of its reviewers.

Though Buzzillions can’t prevent a person from posting multiple reviews on a product, it does search the site for duplicate content and users can notify the site if they doubt a review’s authenticity. This could trigger an investigation by the site that may involve tracking the Internet address of a reviewer, the times and frequency that a person posted reviews or even calling the person in question.

Buzzillions is particularly helpful when it comes to certain categories of reviews. The Electronics category, for example, is so populous that it must be divided into 17 subcategories with numerous smaller groups in each subcategory. This category can also be searched by brand.

But Buzzillions has its flaws. Not all products can be sorted with personality labels. And I found that some items were miscategorized. A “GPS” category included receivers, car navigation systems and wristwatches, but when I tried to narrow these products by selecting the “Automotive GPS” category, individual GPS data loggers and receivers still appeared instead of car-only devices like those from Garmin (GRMN) and TomTom. Buzzillions said it would correct this error, but products placed in the wrong categories could be highly confusing for someone unfamiliar with a product. Other categories, such as Shoes and Clothing, left me disappointed by the low number of represented brands and subcategories (i.e. shoes didn’t separate heels or flats from the pack).

Nothing is sold on Buzzillions.com itself, though the site does link to partner stores. But some product pages listed only one online store where the item could be bought. Buzzillions plans to fix this problem by listing about five to 10 online retailers per product.

People can use the site in two ways: as members, by signing up with an email and password and entering descriptions to create profiles of themselves and what types of products they like; or as unregistered visitors to the site. I tried both methods and found the member recommendations practical because they pointed out products I may not have found as quickly using searches. As a member, you instantly see a list of suggested products according to your profile as well as receive gift suggestions via email. And even using the site without becoming a member worked well, never making me feel like the best bits were only offered to registered members.

I really liked Buzzillions’ ”Review Snapshot,” a small at-a-glance box that lists pros, cons and best uses for a product. This snapshot also shows a product’s Buzzillions Rank, as well as its star ranking compared with the category’s star-ranking average. I saved a lot of time by skimming these concise snapshots rather than opening every review.

Buzzillions recently created a mobile version of its site, mobile.buzzillions.com, which runs on the iPhone’s Web browser and can be used for quick looks at reviews and top-10 lists. The company has plans to release an actual iPhone app that should be available soon via Apple’s (AAPL) App Store.

The more I used Buzzillions, the more I grew to depend on the site’s signature Buzzillions Rank, which is clearly listed on a big, bright-green badge. The top 10 products in each category are distinctly labeled, with the No. 1 item in a category getting a special ribbon. And this ranking held true to its formula and showed a product’s real standing: I often saw an item with a higher star-rating average receive a lower Buzzillions Rank because they had far fewer reviews compared with products with a higher Buzzillions Rank.

Another helpful stat that Buzzillions displays prominently with each review is the date that it was reviewed. I looked at a pair of tennis sneakers with a top-10 Buzzillions Rank, but some of that pair’s reviews were labeled with dates that were too old to be relevant for me. Electronics fans, of course, would care even more about these dates.

All told, Buzzillions does a good job of balancing reviews and culling the most-appropriate reviews for certain people based on personality traits. It currently has more than 3.6 million reviews, but will most likely continue to grow as more people use and rely on it, making it an even more valuable tool for shoppers.

– Edited by Walter S. Mossberg

• Email us at mossbergsolution@wsj.com. Find this and other columns and videos online free at the All Things Digital Web site: http://walt.allthingsd.com