Apple sings not Hymn
Apple's been back and forth trying to shut down Hymn from working with iTunes purchased music for a while now — remember, they wrote software that strips the DRM code from ITMS-purchased music (like Real's Harmony, which bypasses FairPlay DRM with their own compatible version). Apparently Apple's gone and broken it entirely (again) in iTunes 4.7.1, which means, of course, that it will be only a matter of time before it's un-broken by the Hymn guys, and so on, and so forth. In other words, if you're using Hymn you may want to wait a little while before upgrading to the new version of iTunes — sorry Shuffle users!
