This script will add or subtract a half-star from the ratings of the selected tracks. Ratings with half-stars appear with "1/2" appended to their ratings (see the screenshot). I highly recommend attaching a keyboard shortcut to this script for faster access.
iTunes 6.0.2 or better (I only discovered this in 6.0.2; it may work in earlier versions).
The scripts have also been posted on the Missing Menu Commands page as separate add and subtract actions.
Also see Assign Half-Star Rating.
(Note: In order to launch this PowerPC-era script on an Intel machine, it must first be opened and then saved using Script Editor (AppleScript Editor pre-OS X 10.0) which is located in your /Applications/Utilities/ folder. More information is here.)
Two scripts copy text from clipboard to current or single selected track's lyrics tag
Create playlists by artist
Gather audio tracks whose files contain no artwork metadata
Perform search-and-replace on text in your choice of tags
Display, create text file listing info of dead tracks
Copy chosen tag info from one set of tracks to a different set of tracks