I've been having a quick look at Google's Open Social... They really need to get better documentation so I'm not exactly sure about the fine detail. There are a few bits on developing widgets but nothing at all on hosting them which is a big chunk to be missing in my opinion. Maybe they are holding off publishing to stop a proliferation of social sites popping up and competing with their "launch partners"?

Some other random thoughts:

• You need to implement your widgets as Google gadgets
• All the samples are based on Orkut so it's not clear if a Google account is required - if it is then that's bad
• There doesn't seem to be any sort of download available, probably as the JavaScript is hosted by the Google gadget system

They have been quite clever calling it "Open" Social instead of "Google" Social but it still sounds like a lock-in to the Google gadget system.

The API is really about building widgets to host in existing social web sites - in all not that exciting. What I would prefer to see is a system that allows me to access my social data from anywhere in applications I write - e.g. my blog, Outlook and my phone...

[Edit: having read around a little, Dare Obasanjo says much the same thing but slightly more coherently.]