For our April meeting, Isaac Schmidt gave a nice introduction to Parse.com, which is a web service plus an iOS framework that lets you quickly and easily set up web-backed object storage for your app. They also have Android support and a REST interface but no desktop Cocoa API. I wonder if it'd be worth writing a lightweight wrapper around the REST interface using RestKit.
Parse is really simple and it's free up to 1GB of disk storage and 1,000,000 server requests. If nothing else, I can imagine using it for quick prototyping or lightweight custom applications. As someone who has yet to dive into iOS development, I like that this will make it easy to get something working that's a real web-backed app.
Isaac demoed an example app called Instazam. (If that sounds like the name of a company that recently sold for a billion dollars, that's no coincidence.) Here's a zip file containing Isaac's Keynote slides and the Instazam code. You can also see his slides embedded below.