My girlfriend has an iBook, so I'm not sure if this is something that has happened on other configurations, but she said to me today that iTunes was acting quite funny. It seems it was starting at about a two minute interval with no human input -- even if the computer wasn't being used at the time.
I managed to track the problem down to the Dashboard, of all places. She had the iTunes widget running, and it was paused on a song. Tt seems that that widget was doing a checkup call or something to iTunes, which caused it to re-open. So I had her close the widget, and the problem vanished. I can't confirm if reopening the widget will cause this to continue to happen.
[robg adds: I tested on my PowerBook, and I couldn't get this problem to recur. Regardless of whether I paused a song with a widget or iTunes, when I quit iTunes, the widget's display changed to read "iTunes is not open." I'm publishing this on the hopes that perhaps someone else is having this issue, and we may be able to figure out if there's other software involved.]

