One thing that I used to like about KaZaa and Napster (back in the day) and the old morpheus was the "find more from same user" feature, and also the ability to chat. This is very nice as it really adds a community feel and is useful for finding new files (instead of just downloading files your already know about.)

I realize that this is a lot of work but it is something which would be nice to see sometime in the distant future...