Socialmod is a system to either automate or simplify your site's social content moderation. Its socialmod API allows for direct integration of socialmod into your site, making using their service far easier. Its service has been used for such high-profile sites as the BET.com awards, as described in its blog.
Discussion of Google's recent acquisition of Jambool has largely centered around its virtual currency platform, Social Gold. The power behind that platform comes in the form of the Social Gold API. Again, Google has bought a company whose API is central to its success.