Andrew Kaplan has just started Facebook Enthusiast and he's got a new post on 10 Reasons for the LinkedIn Crowd to Spend Time on Facebook
Where LinkedIn is more like being in a business meeting, Facebook is more like a block party.
I think this is a very good differentiator between the two. Facebook has all sorts of things going on, and application developers keep adding more. And, of course, people are jumping on the bandwagon (30 million now) just like at those big block parties. But LinkedIn isn't a schlump. What it lacks in shiny, new features it makes up for in laser focus. LinkedIn is designed to help business people make connections to one another. Period.
This actually leads to some head scratching, though. Beyond connecting Jack and Jill for business, there is very little "social" going on here. Even the "groups" in LinkedIn aren't terribly social. What does a social or business networking group "do" with LinkedIn groups? Those "groups" defined loosely as alumni (college or business), the groups feature makes a lot of sense, as it enables distant colleagues to make a connection via their common history. This doesn't directly benefit the group - it makes members of the group visible to the group, and they connect via the standard LinkedIn mechanisms. But if the group is already fairly cohesive and has an online presence already, I can't see much point in setting up a special group in LinkedIn. I asked about this on LinkedIn and didn't get anything terribly insightful as an answer.
All said, I think the laser focus is a core benefit of LinkedIn. Sure, you make your network visible to your connections and find people, but the networking and connections need to be made on a one-to-one basis and that happens over coffee or email, not within LinkedIn itself. And this is why people who want the social are attracted to places like Facebook. I wonder if those same people will jump to the next block party?