Google is holding a press conference right now, and it appears that they have everybody's support for the new Open Social API in an attempt to stem the popularity of Facebook among 3rd party Web 2.0 application developers. Supporting sites include MySpace, LinkedIn, Plaxo, Friendster, etc.
UPDATE: Full text of press release here.
TechCrunch has reported on this topic before and has some details on what the APIs contain.
I haven't seen the actual Open Social API documentation yet, but I bet it'll be using XML all over the place. Good news for the XML Aficionado... ☺