Back in the day, we had to keep our cover art to a certain size, else our players might not display it. I used an old Sansa Fuze, and learned to keep my artwork at 200 by 200 pixels or less, or roughly less than 25KB in size.
I doubt this is much of a problem with today's portable devices, and am curious as to the size most people are settling upon.
Also, when trying to find these forums, I also came across this user report of a serious bug. This was a while back. Has the issue been resolved?