First of all: a very nice app.
Here are my mac's features: 800Mhz PowerPC G3; 128 MB; 18 GB diskspace:
1. At the end of a song the cover is changing. That's all OK, but until the appearance of the cover of the next song dures about 10 seconds in general while the song struggles and interrupts several times due to cover loading. A bug to be fixed as soon as possible!
2. The playlists of the back covers are either incomplete or list songs of other albums. (For example, I got an album called "Live!" by Bob Marley and an album called "Get Down Live!" by KC and the Sunshine Band. When I play a KC song, the playlist gets mixed with Marley songs) A bug to be fixed in the near future.
3. There are the options to see on the back cover a) just the song name, b) song name and track number, and c) song name, track number and running time. But there's no option to have just the song name and the running time. A feature to be included, if possible.
4. The loading time of the covers are quite OK, but when a song has no cover image in the iTunes cover box in the lower-left part of the iTunes window and I activate JewelCase, then the loading time of a one-color cover is very long. After deactivating JewelCase, iTunes goes on much slower than it did before activating JewelCase. An annoying bug to be fixed as soon as possible.
Overall, I must say, JewelCase has had a very good beginning, but for me it's important to see these 4 bug observations being fixed. Then, I'd say the plug-in is really an useful funny thing. I hope the developers are going to fix these bugs soon.