This script will apply user-entered text to the "Category" tag of each of the selected tracks. iTunes 5 or better.
(Note: In order to launch this PowerPC-era script on an Intel machine, it must first be opened and then saved using AppleScript Editor, which is located in your /Applications/Utilities/ folder. More information is here.)
Continuously update your desktop picture to current track's artwork
Delete characters from the beginning or ending of selected tracks' name, artist, album, comments, composer, or show tags
Copy multiple playlists from iTunes to iPod
Change the settings of hidden iTunes preferences
Displays files in iTunes Media folder not in iTunes track library
Perform search-and-replace on text in your choice of tags