I saw this information on a post over at Cameron O'Reilly:
Okay, so here's a tip for you iPodders out there - if you find a mysterious iTunes folder on your hdd and it's got nothing but .tmp files in it, ahem, DON'T DELETE IT.
I keep my music in a special folder on my hard drive, NOT under "My Documents/ My Music" which is where iTunes likes to try to stuff it. So yesterday when I went to PUT something into My Music, I discovered an iTunes folder in there. Hmmm, I thought to myself. What's THAT doing there? Must be junk DNA, I thought, from when I installed iTunes. I checked inside it, about 7000 .tmp files, taking up space, so, I thought, fuck it, I'll just delete it.
Next thing I know? My iPod is EMPTY dude. All gone. So, I re-import everything from my REAL iTunes folder, no big deal. BUT... all my meta-data is gone. Genres I changed are all back. NO SMART PLAYLISTS. NO RATINGS. 6 months of engineering my iPod to be the way I want it, all up in smoke. Time to start again.
I normally wouldn't quote an entire post, but I know a lot of people that do not store their music in the default folder. All of my iTunes music is stored in an external hard drive on my Mac, but I also keep music in a different partition from the My Documents partition on my Windows machine; after reading this post, I checked My Documents/My Music and sure enough, there were .tmp files in it.
Anyone know a way to get around this on the Windows platform? Anyone back up their .tmp data in case this happens?