My friend Rich Skrenta has a typically cogent post up, only this time it's not about the Google OS, it's about the me-too and I don't wanna be left out network effects of digerati flocking to Facebook. In particular, Rich notes how the switching cost is pretty low for most SN services.

Some quotes:
"In an environment where travel is free and instantaneous, you get flash mobs.
If a place is cool, or new, or interesting, you go there to check it out.
A place might be interesting simply because there are a lot of other people there at the moment. "

and

"It's easier than ever to move from one service to another. Blog reader? No problem. Photo site? I have accounts on all of them anyway. Social networks? Yeah I'm signed up on all of them. I use the ones everyone else is using, at the moment. Just like we all do. The rest have a stub profile for me, but don't see much activity."

Susan sez:
The portal play was to embed all your apps and tools in one place as a way to hold you there(think AOL on the web).
The social network play was to have you collect all your connections to hold you there (think LinkedIn.)
The widgety-goodness way (I just can't write Web 2.0 one more time!) is to try to get the users to aggregate their tools, services, and connections in one place (think Facebook today).

That's all cool but the other thing web businesses need to think about, besides widgets, is the identity issue--the services that can figure out aggregating tools and services --like Facebook is--will grow, but the ones that can also figure out identity management--as in multiple identities and layers of privacy--can leap ahead.