Social Search, at least at first, will be able to include results from Twitter, FriendFeed, Picasa, Blogger, and Google Reader.
The last three are obvious since Google owns all of those. Twitter seems obvious too because of the new Google/Twitter search deal. FriendFeed is an interesting one though since Facebook bought that service in August. As expected, it doesn’t appear that Facebook data will play a big role in Social Search (if any), as Google and Facebook continue their social profile stand-off.