I also just installed Rockbox on the Clip Zip. Other than finicky USB connection issues, I had no problems. Album art doesn't seem to work. At least not for my files, where the album art is embedded in the mp3 files. Actually, I thought I read that album art won't work if they are over 75kb, and I'd say most of mine are way more than that, like 500kb. lame.
but a couple of those themes are amazing. What people do with 96x96 pixels is impressive.