How many of them are active? 7? I've never used it. None of my friends use it. I know a handful of people with accounts, but they never actually use it.

Interesting possibility, but I'm not completely sure this would work. I'm sure that a "jobs" section of facebook would gain plenty of interest, but I think LinkedIn appeals to people who would like to keep their job-related networking completely separate from their social lives.

The line between professional and personal life will shift, and this may be a generational thing. But who knows, the distinction may sharpen rather than blur. One of the big reasons I haven't left a huge web/video trail of my own stupidity on the web is that I'm old enough that the web was still an infant when I was in college, and nobody had cell phones with video cameras and recorders. Now, anything even slightly unusual on a college campus will be recorded by at least a half dozen people.

You could figure that people will blend social and professional lives as they they get more casual about these artifacts. But maybe they'll just learn to draw very fine and deliberate distinctions - kind of the difference between getting excessively drunk at a work event and getting blotto at a bar where your colleagues just happened to show up later in the evening.

Anyway, I went a little off topic there, but maybe there's a long term niche for social/professional networks that are explicity not social/casual.

I hear this a lot and in my opinion, a sizable minority of people can't mix their social and professional networks together. I can't have my business clients see who I'm currently dating or pictures from my nephew's bar mitzvah. Not only is it unprofessional, but it can harm my future dealings with them.

I know a lot of people have on Facebook have accepted invites from their boss or professional contacts and they stop participating in it as a social network and start using it as a glorified email/im system. If everyone did this, it would harm Facebook's ecosystem in the long run.

Even with privacy controls and grouping people together, keeping mental context about who can see what at any given time is just too hard for most people. Seeing facebook.com and thinking social and linkedin.com and thinking professional is far easier.

* Disclaimer - I used to work for LinkedIn in analytics as a product manager and did a lot of user interviews, but I may have drank the kool-aid.

I thought it was more that it's for people that are too busy for social networks; those who want to be found and to browse some structured information on other people in their field without the time sink of status updates and shared media.

I know lots of people who have found jobs or been recruited off of LinkedIn--it's alive and well.