Defensio, the anti-spam service, offers an API that can be integrated into blogs and web sites to fight spam comments and other unwanted spam (details at our Defension API profile). The service appears to be run by a small team, and is similar in purpose to Akismet, the much larger spam filtering service from Automattic (which powers WordPress.com), who also offer an anti-spam API.
Why did Pinterest remove its API documentation earlier this year? Well, apparently there is no rush to release an already developed API to the public yet. In fact, it may not be released for a while as Pinterest wants to avoid re-tweeting the #mistakes Twitter made in its infancy.
With Instagram's new App update, the "find your friends" on Twitter is very obviously missing. This is due to restrictions from Twitter's side, and seems to be a snub in Instagram's direction as many apps like Foursquare still have access to this part of the API.