I have about 3000 songs in my iTunes right now and about 2000 of them are rated by me on a 5-star scale (mind you I've deleted a lot of 1 star songs too):
1 Star (Going to be deleted 'cause I'll never listen to it)
2 Stars (not horrible, but don't care for it either, ok to shuffle through)
3 Stars (decent song, kind of a catch all good song category)
4 Stars (very good song)
5 Stars (Great song)
Now it's relatively easy for a song to obtain...