The official info page is up. Hmm --
OpenSocial is built upon Google Gadget technology, so you can build a great, viral social app with little to no serving costs. With the Google Gadget Editor and a simple key/value API, you can build a complete social app with no server at all. Of course, you can also host your application on your own servers if you prefer. In all cases, Google's gadget caching technology can ease your bandwidth demands should your app suddenly become a worldwide success.
Nice of the everybody-but-Facebook gang to give this power transfusion to Google.