Music & iTunes Match
I didn't expect the Music app to force quit or error out on me at all, but it did. Unfortunately, those weren't the only problems I had with it.
One of the big new features in iOS 6 is the implementation of music streaming via iTunes Match, direct to your linked iDevice. Currently, iTunes Match is the default play method, even if the music you're interested in is on your device.
That doesn't mean that the device streams everything. What seems to happen--I can't be sure because the app was so unstable--is that Music taps your music locker stored in iCloud before it plays the track. If you have a decent Internet connection, you hear the track. If not, you might or might not hear the track, even if that same track is on your device.
The more I use my iPhone 4S with iOS 6 Beta on it, the more I see of this behavior, especially after long stints of listening to music, and only with tracks that I purchased through the iTunes Music Store. Tracks that I ripped from CDs that I own, whether they're in iTunes Match or not, seem to play on the device consistently without issue.
After an extended period of time playing music or after a number of different applications have been used in rapid succession (perhaps when memory is low), Music will either force quit, or more likely, refuse to play DRM'ed music. Every time I've looked at the device when this happens, I have a low (one or two bars) cellular or Wi-Fi signal. I suspect that Music is trying to validate the license required to play each song, regardless of whether or not it's actually on the device. When it can't make the verification, the song refuses to play.
This would be exactly what the RIAA wants to happen. However, from an iPhone experience perspective, it totally sucks. The way iPhone and iTunes work, I can't have the track on my device without being authorized to play it. If I have a song on my device, there's no reason why I should want iPhone to stream it for me.