I use ratings a bit differentely than others. I've got about 7,200 songs in my library. I have about 1100 songs rated. I have a smart playlist called "Good Stuff" that includes everything that has a rating. When I just want to listen to songs I know I like, I'll just set Party Shuffle to play that. The number of stars I give it doesn't really matter much, just a way for me to know how much I like that song. When I'm feeling adventerous, I set Party Shuffle to play a smart playlist I have setup called "Never Played" which has songs with a play count of 0, and as I listen to them, if I like them, I'll rate them, and they'll get added to the Good Stuff list.
As far as genres go, every song in my library is tagged with a genre, although, I don't really use them. I just assign what I feel fits the song best just because I'm anal about having all info filled in. Getting all of the years filled in next, I have a smart playlist that has everything without a year and when I have nothing better to do, I'll go through and add the year to some songs until I get bored with it, and come back later. Eventually I'll get that playlist down to nothing.