Just opening this as a placeholder. Pianobar is switching to the JSON api as it's figured there will be less chance for breakage there due to its use in embedded device. JSON API documentation has been started by PromyLOPh. Also the big set of commit changes from the merge into Pianobar master is pretty easy reading.
Pianobar now has a dependency on gcrypt due to use of blowfish encryption. MulleCipher appears to be an Objective-C implementation of BlowFish and might serve the purpose. Drawback is that it hasn't been updated since 2002 so not sure how nice it'll play with new XCode, ARC, etc. Haven't looked at the code at all. Could just use gcrypt...
Can't seem to find a download of MulleCipher aside from downloading files individually on Koder.com. Also, personal blog entries by the maintainer say that parts of MulleCipher fail on i386.
I don't think that'll be too much of a problem, I'm sure there's at least one open source implementation of blowfish which can be found so that gcrypt doesn't need to be depended on.
Currently I'm swamped with finals and end-of-year things, but this looks really promising, and I definitely plan on making a transition at some point. I won't fully change over to the new API until all methods are supported, but it looks like pianobar is doing a fantastic job at doing that.
Move over to using the JSON API
Hopefully this API is more stable than the XMLRPC one because it's used on
devices which aren't quite as easy to update.