Though I've not actually used it (yet) I have to thank Chad for the heads up on BoxyTunes; an iOS app that syncs with your Dropbox account and lets you play music and create playlists from your cloud storage. From the description I'm not entirely convinced it is the be-all, end-all solution to the cloud music player but it's one of those underdogs that I'm happy to see in the running. Read more here, get it here.