New with the current iTunes (7.6.1, or could have been earlier) apparently you are able to search by star rating. All you have to do is simply go to the search box and type in a “*”, the more you type in the higher the rating.
So for example lets say you have the song “Like a Rolling Stone” by Bob Dylan rated as 5 stars, and no other song in your library was rated as a 5; you could search: “*****” and “Like a Rolling Stone” would come up.
[Via: Mac OSX Hints]
