Can you clarify how this might work? How will it know how much I like a song? Just because I listen to one song 20 times and another song once doesn't mean I like that song 20 times more than the first one... Would you use the Plays and Skipped fields? Would it use Time of Day as a variable? Will it try to make decisions like "well he listened to this and then this, so now he wants to listen to that."?

I think a ratings system is clear-cut and understandable. It's more like how a radio station might work, certain songs get into heavy rotation, others only occasionally played, etc. If a particular song falls out of favor, you can just turn down the rating a few notches... Plus it's more easily combined with the custom shuffle modes that already exist.

Obviously, it has the major drawback that it requires manual entry of the ratings, but that gives you more control of which songs get more weight, rather than letting the algorithm try to figure it out. I just don't understand how the algorithm would work in practice... Any ideas?