Dont animate items that when neithe rthe old or new y position is within the visible area of the playlist. This change actually makes the playlist usable with a large number of tracks (I tested it with just over 3000 tracks).

The only really bad performance problem with the playlist right now is collapsing and expanding albms wiht a large umber of tracks. 10-20 tracks are almost instantanious, but collapsing someting with about 100 tracks (yeah, kind of a corner case) takes 10-20 seconds...