I only have complete albums, which makes it a little tricky. Some albums *glares at David Bowie and Tom Petty, two terrible offenders* suffer from massive amounts of filler. Others don't. Anyway, I keep all the songs, no matter how lousy.
0 Stars -- means it's unrated, natch.
1 Star -- everything is at least this high.
2 Stars -- In the best 75% of my music. (It's much better for me to use numbers and logic to quantify my appreciation for a song. It keeps the ratings useful and the ratios apt)
3 Stars -- In the top half of my music.
4 Stars -- In the top 25%.
5 Stars -- In the top 10%.
Also, I do an album rating. For this, I add together the ratings of all the songs on the album and divide by the track number. Simple, no? I then multiply the number by ten and put it in the BPM field (ie, 45 = 4.5 stars). Theoretically, this would yield a 0-5 scale, but it really yields a 0-4 scale. Still, only a few bands (Nirvana, Leonard Cohen, Pink Floyd, Velvet Underground, etc) are in the 4-star category. The rest of them are distributed much like the song ratings -- 10, 25, 50, 75%. Might seem brutal for me to have a lot of 1-star albums, but I'm a pretty harsh critic and I have a lot of music
Of course, this system will likely change, at least in ratios. I'm rebuilding my library from scratch right now with lossless, good album art, meticulous ratings, etc. Mostly what I have right now are my favorite albums of all time as well as those that are just lying around -- so these ratios are pretty skewed no doubt. Instead of 10, 25, 50, 75, I'd like to have something like 5, 10, 20, 40, 80.