AutoRate

AutoRate application automatically sets the rating for selected tracks in your iTunes library according to how often each track is played, and how often each track is skipped relative to the rest of your library.
It uses a 10 bin normal cumulative distribution based histogram to automatically scale the ratings so that the mean rating is ~3. Optionally you can use a linear scale with manual shift, scale factor and mid range skewing.
Both the track play count & skip count are used in conjunction with the length of time each track has been in your library to determine, on a relative basis, how much you like each track. Ratings become dynamic and change with your taste in music following how you listen to your songs.
Complete ratings allow you to quickly select playlists of songs that you like.