Indeed, people do seem to be separating their online professional identities from their personal identities more than they used to, now that the tools are available. Web users increasingly use LinkedIn to sign in to business-oriented sites, according to the social toolmaker Gigya.

LinkedIn started offering its credentials as a Web sign-on system early last year, and many business-oriented sites now offer users the option of authenticating using their LinkedIn account in addition to other options like their Twitter and Facebook accounts.

Gigya has seen a major increase in LinkedIn log-ins to sites it identifies as business-to-business. Twenty percent of social logins on such sites used LinkedIn credentials in January 2011, up from three percent in July 2010.

LinkedIn accounted for 26.6 percent of social sign-ons in January on the stock market news site Seeking Alpha, 20 percent on the Harvard Business Review and 14 percent on the Internet Advertising Bureau site. (The rest of social sign-ons were through Facebook and Twitter, mostly.)

To be sure, LinkedIn is still a minority share of social sign-ons on such sites, and these numbers don’t include users who register for a site without the help of a social network, or users who visit without registering.

Plus, the trend may be headed in the other direction. Many people propose that our personal and professional identities will increasingly merge, especially for younger generations. That’s the theory behind the legion of LinkedIn 2.0 start-ups like BranchOut and Assetmap.

LinkedIn is the first major U.S. social networking site to file for an IPO. It hopes to raise $175 million.

Among the topics we discussed were the rise and fall of social networking sites and whether that makes them fads, the implications of oversharing from a young age and the potential for social networks to become more productive and engaging.

It was a fun chat, and you can now listen to it and read the transcript online.

You can also read my recent trend story about multiple online identities that helped spark the conversation.

Although he later clarified, “I wasn’t making a value judgment,” maintaining multiple identities, whether it’s as simple as publishing some photos to Picasa and others to Facebook, is becoming a big trend in online life.

Even as Zuckerberg’s Facebook extended its dominance in 2010 to the point where it seems to have a social Web monopoly, it was still a landmark year for social network competition.

Where in the past, tech industry watchers derided new start-ups for launching “yet another social network,” ever more users seem to be constructing multiple online presences that utilize the strengths of various platforms and networks.

And this splintered approach is only going to increase.

Internet users now have plenty of outlets for self-expression. They can prioritize individuality and choose to post on the highly customizable Tumblr, or instead value the comprehensiveness of a network and post on the blander Facebook.

A big part of this shift toward understanding the private online self versus the public online self has been the rise of Twitter. On Twitter, regular users make the sort of decisions celebrities do: What to share about their private lives with their public audience of followers.

Another shift has been the rise of smartphones, along with their quality broadband connections, good cameras and mobile apps.

As an early adopter of various social apps, I’ve recently been confronted with the choice of whether to post a picture taken with my Apple iPhone on-the-go to Facebook, Twitter, Instagram, Path or Picplz.

Each of them has different audiences, different associations with my personal or professional identities, and different expectations for how people will view and interact with my snapshot. (And I suppose there’s also the option of keeping the pictures to myself on my phone storage.)

Although the people noisiest about privacy on Facebook have at times been the media, publicity of the company’s highly confusing privacy settings seems to have led to many more people being aware of them and perhaps even changing them.

Perhaps that’s why I see an increasing–but still quite small–portion of my Facebook friends using pseudonyms on the service. And when I asked them why, I heard a variety of reasons.

One is a teacher, another prefers to go by the moniker he uses artistically. Yet another is a college student who is applying for jobs and who wants to be more anonymous for a while. Like many of today’s young people, she has become highly conscious of balancing the freedom to be herself online with the way she is perceived by professional contacts.

(A representative for Facebook declined to comment on whether the company has recently been more permissive about allowing pseudonyms, something it has traditionally frowned on.)

Of course, very little of what’s posted online can be trusted to never get out or never be linked to its originator. If you really want to keep your thoughts private and impermanent, of course, keep them in your head.

But there are now many more options for more private communication, many of them having first come out in 2010. They include small-group coordination tools like GroupMe, Fast Society and Beluga. There’s also Path, a start-up from a former Facebooker that is perhaps too limited by design, but is exploring the world of more intimate and personal communications.

For many people, their Facebook network is far from a direct match with their real-world friends, so it will be increasingly important to use these tools to dice circles up and make them more accessible. (Facebook is also trying to address that need with its own Groups tool.)

To be sure, that Facebook map of connections is a highly valuable asset, one the company has fiercely protected, as Google reformulates its approach to the social Web.

Splitting your users into an entirely new social graph will certainly hamper growth. For instance, another early Facebooker launched Jumo, a social network for people connecting with nonprofits that seems to risk being redundant with, and isolated from, similar efforts on other platforms.

And Foursquare, despite its zeitgeisty innovation for sharing real-time location updates, has accumulated only about five million users in the last two years.

However, the speedy growth of new social networks like the addictive Instagram–which is like Twitter for pictures and got one million users in its first two months–shows that there’s still an opportunity to take an independent path.

What seems particularly notable about the current moment is that many people are evolving their approach to expressing themselves online, and they now have many tools and contexts to do so. And it’s up to them if these multiple identities will be unified anywhere except in their heads.

(Image collage at top of post courtesy Flickr user shannonkringen.)

Please see the disclosure about Facebook in my ethics statement.

An interesting variation on the “membership drive” and one that’s gotten Tagged in hot water with New York Attorney General Andrew M. Cuomo, who intends to sue the company “for deceptive e-mail marketing practices and invasion of privacy.”

“This company stole the address books and identities of millions of people,” Cuomo said in a statement. “Consumers had their privacy invaded and were forced into the embarrassing position of having to apologize to all their e-mail contacts for Tagged’s unethical–and illegal–behavior. This very virulent form of spam is the online equivalent of breaking into a home, stealing address books and sending phony mail to all of an individual’s personal contacts. We would never accept this behavior in the real world, and we cannot accept it online.”

Tagged, for its part, claims this is all just a big misunderstanding. In a statement of its own, the company denied abusing its users’ personal address books, saying, essentially, it had their consent to do so.

“When our company tested a new registration process, we discovered that our ‘invite your friends’ language was confusing,” said Tagged CEO Greg Tseng. “…In no instance did Tagged access a person’s personal address book without their consent and no emails were sent without the person giving us permission. We realize that some were confused and accidentally agreed to invite their friends.”

Oh, and next time you register for a social network, be sure to read its Terms of Service–especially the portions that are presented in ALL CAPS. They might be important. From Tagged’s Terms of Service:

“E) Notice Regarding Commercial Email

MEMBERS CONSENT TO RECEIVE COMMERCIAL E-MAIL MESSAGES FROM TAGGED, AND ACKNOWLEDGE AND AGREE THAT THEIR EMAIL ADDRESSES AND OTHER PERSONAL INFORMATION MAY BE USED BY TAGGED FOR THE PURPOSE OF INITIATING COMMERCIAL E-MAIL MESSAGES.”

An interesting variation on the “membership drive” and one that’s gotten Tagged in hot water with New York Attorney General Andrew M. Cuomo, who intends to sue the company “for deceptive e-mail marketing practices and invasion of privacy.”

“This company stole the address books and identities of millions of people,” Cuomo said in a statement. “Consumers had their privacy invaded and were forced into the embarrassing position of having to apologize to all their e-mail contacts for Tagged’s unethical–and illegal–behavior. This very virulent form of spam is the online equivalent of breaking into a home, stealing address books and sending phony mail to all of an individual’s personal contacts. We would never accept this behavior in the real world, and we cannot accept it online.”

Tagged, for its part, claims this is all just a big misunderstanding. In a statement of its own, the company denied abusing its users’ personal address books, saying, essentially, it had their consent to do so.

“When our company tested a new registration process, we discovered that our ‘invite your friends’ language was confusing,” said Tagged CEO Greg Tseng. “…In no instance did Tagged access a person’s personal address book without their consent and no emails were sent without the person giving us permission. We realize that some were confused and accidentally agreed to invite their friends.”

Oh, and next time you register for a social network, be sure to read its Terms of Service–especially the portions that are presented in ALL CAPS. They might be important. From Tagged’s Terms of Service:

“E) Notice Regarding Commercial Email

MEMBERS CONSENT TO RECEIVE COMMERCIAL E-MAIL MESSAGES FROM TAGGED, AND ACKNOWLEDGE AND AGREE THAT THEIR EMAIL ADDRESSES AND OTHER PERSONAL INFORMATION MAY BE USED BY TAGGED FOR THE PURPOSE OF INITIATING COMMERCIAL E-MAIL MESSAGES.”