@dlowan,
I have similar problems and am still trying to isolate the root cause.
Here are a couple of things to try though:
1 try plugging directly into the comPuter and bypassing the USB hub.
2 turn off syncing for photo's, then sync, then turn them back on again and sync again, it sometimes works.
3 go to the iTunes music folder and delete the cache. Then try sync again.
Some people think it is corrupted photos which cause the problem. Others think it's a USB hub issue.
Are you using a USB hub?