iTunes won't quit

Fluther: ITunes restarts when quitting.

This one bit me: If you have SRS's iWow installed, it can get in a mode where it will restart iTunes almost instantly when you quit the app. You're left with a transparent iTunes icon in the Dock. Even trying to kill the iTunes (and iTunes Helper) process from the command-line doesn't work.

The trick is to also kill the 'genredetection' processes through Activity Monitor or the command line, which will (finally) let the app quit.