I just installed Jaguar on a computer here at work. First thing I did was drag my music folder into the iPod library. After waiting for a while, it began copying files. I was like, "what the hell?". After a little bit, it gave me an error that I had run out of disk space.

Only after doing some searching did I find that iPod automatically makes copies of the files into it's own folder in order to "centralize" your music files. Luckily, there's an option to turn the copying off. What a pain, though. I had to go find where it had made the copies and delete them.