Last fall, a small but vocal group of Twitterers managed to shame Johnson & Johnson (JNJ) into apologizing for one of its Motrin ads.

This weekend’s replay: a howl of outrage, amplified and directed via Twitter at Amazon (AMZN), which may or may not have instituted a boneheaded policy  regarding “adult” books on its site. Or “adult” books aimed at gay and lesbian readers. Or something.

What happened? It’s not clear. But search for “#amazonfail” on Twitter and you’ll find that many Twitterers believe that Amazon has stripped the sales rankings from all manner of books that deal with gay and lesbian, and/or “adult” topics, making them less likely to appear on the site. In essence, the Twittersphere charges Amazon with trying to hide material it finds distasteful or that it thinks some customers will find distasteful.

Example: Amazon’s listing for Annie Proulx’s “Brokeback Mountain” doesn’t have a sales rank. But the author’s newest book does have one.

From what I can tell, the meme started up on Saturday, but didn’t start building steam until Sunday afternoon, when I noticed mild-mannered types like New Yorker writer Susan Orlean railing about Amazon on Twitter.

And it’s still going. As I type this, after 10 p.m. Eastern on Sunday night, the “amazonfail” keyword is generating a dozen hits on Twitter’s search page every couple of seconds.

Amazon hasn’t helped its case by remaining more or less mute throughout the weekend. But, by Sunday evening, the retailer had issued the same line to me and several other reporters: “We recently discovered a glitch to our Amazon sales rank feature that is in the process of being fixed. We’re working to correct the problem as quickly as possible.”

Not a terribly illuminating response, and I’ve asked for more information. But no matter what really happened, Amazon now has a real problem on its hands: A vocal group of people believe the retailer has discriminated in some way against gays and lesbians.

When Johnson & Johnson got caught in the Twitterstorm last fall, it had a relatively easy way out: A profuse apology to people it had offended. But Motrin has a very specific customer base and Amazon has a much broader one, and anything it says or does regarding gays, lesbians and “adult” material of any stripe is bound to upset some people.

But the company should do the right thing and clear the air anyway.

UPDATE: Here’s an apology from Amazon, which doesn’t really explain what happened, but says the problem didn’t just affect books aimed at gays and lesbians.

BoomTown reported Monday in a major scoop that Yahoo’s (YHOO) Jerry Yang will indeed be stepping down as soon as the Yahoo board can find a suitable replacement. Digital Daily argued that it was perhaps the best thing Yang could have done for the troubled company. Early trading on Tuesday saw a 14 percent rise in stock price–an addition of nearly $2 billion to Yahoo’s market cap. Happy days didn’t last long, of course. All it took was a statement from Steve Ballmer reasserting Microsoft’s (MSFT) lack of desire to buy the company to send its share price plunging to $9.

Microsoft is allegedly coming close to settling on a new head for its digital business, not for lack of lost time, though–BoomTown predicts the winner will be Qi Lu, Yahoo’s former head of search. We’ll know soon, supposedly. In the meantime, Microsoft is busy trying to woo Verizon Wireless (VZ) away from Google (GOOG) as its default search partner on many of its devices. It’s willing to pay from $550-$650 million–twice as much as Google’s paying, allegedly–to own 60 percent of all searches made from mobile devices.

Digital Daily had more news of the continually declining economic situation (OK, econalypse). This week, the harbinger of doom was the precipitous fall in corporate IT spending, which will be, uh, about $0 over the next 90 days, according to Changewave. That just about lines up with the fact that online spending is at its lowest level in seven years. Meanwhile, concerns that current economic conditions will last much longer than previously expected prompted a tech selloff that kicked tech’s ass all the way back to 2003. Good times.

On a happier note, now everyone knows how to make serious cash from social media: Run for president. In the 21 months of his campaign, Barack Obama’s online machine raised half a billion dollars. Listening, Mark and Chad? How not to make money: Ask Axl Rose. In a pioneering move, the fabled Guns N’ Roses album, “Chinese Democracy,” launched on MySpace (NWS). Not so pioneering: Crappy sales. Of the tons of fans who tuned in, less than tons bought the album. In a nonsocial-networking move, YouTube will host its first-ever offline party in SF this weekend–Obama Girl, Fred Figglehorn and other viral phenoms will be in attendance. Don’t worry, BoomTown is going so you don’t have to.

MediaMemo followed the burgeoning saga of Mark Cuban’s battle with the SEC on charges on insider trading–more to come, no doubt. Motrin was also in the hot seat this week for its insensitivity toward women in its recent campaign aimed at, well, women.

Walt Mossberg gave Research in Motion’s (RIMM) BlackBerry Storm a comprehensive review on its launch date. For the smartphone’s details and a video of of its many features in action, check out Personal Technology. Covered in Mossberg’s Mailbox this week were some pros and cons of buying an e-reader, and details about the lack of FireWire as a stumbling block for buying a new MacBook (AAPL).

In The Mossberg Solution, Katherine Boehret takes a look at VideoSurf, a video search engine that searches videos by “seeing” the images that appear in them.

(Note about the placement of stock symbols: MySpace is owned by News Corp., which also owns this Web site, and the MacBook is an Apple product.)

The story: Big pharma Johnson & Johnson (JNJ) has rolled out a Web clip (below) in which a snarky, knowing commentator gripes about the social pressure to “wear” babies in slings, carriers, etc–and the Motrin-ready aches that “wearing” a baby can cause. And in the last few days lots of blogger/Twitterers have agreed that:

• The ad is offensive.
• Motrin/JNJ doesn’t “get” social marketing.
• Something should be done! Maybe a boycott.

How many bloggers/Twitterers are actually complaining about this? And are there enough to hurt JNJ, which made an estimated $1 billion in profit from Motrin each year? Mmmmmmaybe.

Tools like Google’s blog search and Twitter’s Summize search will tell you that, yes, some number of people are chattering about this on the Web. And as of 8:07 a.m. Monday, the Motrin.com site was down, whatever that means. But from what I can tell, only a few thousand people have actually seen the ad on Google’s (GOOG) YouTube. I’ve asked video watcher TubeMogul for info on the ad’s audience and will update when I get it.

But even if the outrage is widespread, it’s going to be hard make a connection between online chatter and real-world results. Otherwise Ron Paul would be the 44th President of the United States.

Meanwhile, at the risk of a cyber-stoning, let me say that I don’t think the ad–which seems to be aiming at the same set of people who buy very expensive strollers but feel a bit conflicted about doing so–is an outrage. And neither does the person who does most of the baby-wearing in my house.

I ran it by her in the twilight hours this morning, between feedings, and she shrugged: “It’s true.” Then she went back to sleep.

UPDATE: Twitter Moms unite! JNJ has apologized, and is very, very sorry. Kathy Widmer sends Forbes.com this mea culpa:

I am the Vice President of Marketing for McNeil Consumer Healthcare. I have responsibility for the Motrin Brand, and am responding to concerns about recent advertising on our website. I am, myself, a mom of 3 daughters. We certainly did not mean to offend moms through our advertising. Instead, we had intended to demonstrate genuine sympathy and appreciation for all that parents do for their babies. We believe deeply that moms know best and we sincerely apologize for disappointing you. Please know that we take your feedback seriously and will take swift action with regard to this ad. We are in process of removing it from our website. It will take longer, unfortunately, for it to be removed from magazine print as it is currently on newstands and in distribution.”

Lesson: Carping on Twitter does indeed work. Sometimes.