For the developer seeking to experiment efficiently with social APIs, O'Reilly's 2nd Edition of "Mining the Social Web" is a truly outstanding resource.
Author Matthew A. Russell drops the developer right into the sandbox of each social network (Twitter, Facebook, LinkedIn and Google+ are particularly emphasized, as you would expect) with just the right amount of explanation about what's accessible via each dataset, and then clears out all the obstacles so they can start data mining against very clear examples.
After our recent look at the growth of social APIs, we thought we'd look back at the history of the category. We added the Plazes API in September, 2005. In terms of the web, this is recent history. In terms of APIs, we might as well be looking at scrolls. In fact, less than half of the first 10 social APIs are still alive today. Below you'll find a list of those trailblazing 10, along with a status for each of them.