[insomniac]

the album art should be named folder with .jpg format. if it is named wrong it wont show, though if you have sense 2.5 you could click update album art in the music tab.
I dont use active synch either, I copy and paste my music along with the album art, so dont really get this issue. A while ago, when I had first got tp1, this happened. there is a cab I used from xda that will pull down album art from google, it very easy to use and doesnt take long at all, works for wm player and tf3d and sense. I think it was called, getalbumart.