Here's an interesting piece from the New York Times that looks at Facebook Connect's growing role as a sign-on / social graph utility. Twitter and Google have similar products. Why is this important? This excerpt sums it up:

Since Facebook Connect was introduced in December 2008, more than 80,000 Web sites and services have put the log-in feature to use, said Ethan Beard, director of the Facebook developer network ... "Facebook is evolving through Facebook Connect into much more than a Web site," said Mr. Beard, who works closely with Facebook's community of third-party developers. "It's also a technology and a service to provide social plumbing and creating a social layer the whole Web can leverage." [Emphasis added.]

These sign-on services, along with other APIs, attempt to achieve lock-in through ubiquity. That's infinitely fascinating to me. Take Twitter, for example. It's become the standard for micromessaging (or microblogging or whatever you want to call it) not by forcing people into a Twitter.com silo, but by allowing the Twitter service to seep into the web's nooks and crannies. Put another way: "platform" is way more powerful than "website."