iTunes 9 (and 10) have faulty issues with iPods now. I do not know why this is happening, honestly, but I have found out how to make mine work perferctly... the only problem is that my album art is corrupt and I'm not trying to fix it cuz it might eff up again. Some songs have the wrong album art and it's quite annoying!
Here is a thread to concentrate on. More people need to be aware:
http://discussions.apple.com/thread.jspa?threadID=2151907&start=0&tstart=0
PLEASE, READ THROUGH THE WHOLE THING FIRST. IF IT'S WORTH IT TO YOU, THEN YOU WILL. Be wary of downgrading iTunes and reformatting iPods. 160GB iPods cannot sync with iTunes Versions less than 9 (maybe some other iPods too). Check yer iPod's compatibility. try to find my posts or wlamar91's posts or mooksmom's posts (near the beginning of the provided thread you can find the other two users'). As of today, mine were on page 48.
i hope yall find some good help. Apple isn't doing anything about it lol. Goodluck.