I haven't got a lot to add to this TechCrunch post other than to say that I find it immensely cheer-inducing. There are a lot of unknowns surrounding the OpenSocial platform, but its looming marketshare at least makes it seem likely that I'll be able to avoid learning any more bowdlerized web technologies with "FB" at the front of their names.
FBML, FQL, FBJS — it was getting out of control, and it all stinks of proprietary lock-in and a rather lame (but admittedly necessary from a security standpoint) attempt to wrap the LAMP stack under a layer of branding. That's not to say that every technology coming out of Facebook is worthless — I've heard some encouraging things about Thrift from people I respect (although if you're not in the market for an especially high-performance RPC framework, using something established like XML-RPC still seems like a better idea to me).
But Google's got a fairly good track record of only reinventing the wheel when they need to build a particularly enormous wheel. So cheers to this potential game-altering alliance. I want APIs, not languages; interfaces, not environments.