Ning has announced they are adding support for the Atom Publishing Protocol:

So that's dealt with getting data in, sharing data between apps - but what about getting data out again? In the talk we proudly unveiled our new Atom API which lets you execute arbitrary queries against the Ning Content Store and get the results as an Atom feed. This means that every app on Ning gets a web services API with full read access without having to add a single line of code. Some of the queries are really nifty, too - here's how we got the list of clones of my NY Trip app. You can subscribe to that feed and be notified every time someone makes a clone. As part of our Atom API support we'll soon be rolling out write access too, using the Atom Publishing Protocol.