I made a comment in passing in a post about Vimeo:

you do know that Facebook is AOL 2.0, right?

I found a post that Scott Heiferman made

While at Sony in 1994, I was sent to Virginia to learn how to build a Sony "app" on AOL (the #3 online service, behind Compuserve & Prodigy at the time) using AOL's proprietary "rainman" platform.
Fast forward to Facebook 2007 and see similarities: If you want access to their big base of users, develop something in their proprietary language for their people who live in their walled garden.

What happens when Flickr and LinkedIn and Google and Microsoft and MySpace and YouTube and MetaFilter and Vimeo and Last.fm launch their platforms

we already have a platform on which anyone can communicate and collaborate with anyone else

It's called the internet

instead of custom applications running on a platform in a walled garden, applications run on the internet, out in the open, and people can tie their social network into it if they want