Facebook has always been known as a walled garden of social data. Until today, the only data you could access was the status updates of the user, and a few other things.
I'm excited to see applications evolve. Popular Twitter desktop client Seesmic has already gotten full support for the Open Stream API.
Facebook has finally grown up and joined the open web. As a developer, what will you build? Or as a user, what do you want to see built?