A couple months back I discovered hymn, which allows one to decrypt AAC files, e.g. from iTunes, and play them back without worrying about DRM. I feel somewhat bad for Apple, since their DRM terms are pretty good relatively speaking, but DRM in general is lame, so that's the way it goes. Apple probably won't care too much since most people don't have the savvy to use this sort of software. Rarewares' software is useful for converting decrypted AAC to whatever format you want.