Don't know about anyone else but I would find it really handy to have a list of your most recently played playlists (maybe the last 10).
Obviously you wouldn't want a playlist of other playlists to appear in it - only the lowest level one which contains the songs. e.g. If your playlists are structured by artist/album then you would only want the albums to appear in it.
I would find this really helpful as I have so many playlists it takes me ages to go through them all to find the album i'm looking for. Maybe I'm doing something wrong.
Anyway, what does everyone else think?