I'm glad to see that I'm not the only one with this problem. I reset my iPhone 4s recently and since then have been unable to sync music. The same music syncs fine to my iPad2. My phone now has no music at all, although photos etc do sync.
I've been on the phone to Apple Care for hours, and so far they have not helped. I've uninstalled and re- installed iTunes. Nothing helps.
Incidentally, when I connect the phone to iTunes it shows up in the control panel, but the little spinning wheel next to it spins for ages, then I get a message saying that iTunes could not sync and I should re-connect or try again later. I ignore this, then the bar at the top says it is synching, but it doesn't.
Has anyone got any ideas? Perhaps I should try resetting the phone again, but I don't know if that would help.