It would be useful if the tray icon tooltip would display album cover art. Technically that would show a window instead of a normal tooltip when the mouse pointer hovers over the tray icon.

This is implemented in last-exit[1] and looks fantastic. The file is last-exit/src/TrayIcon.cs[2]. From what I can tell, last-exit is written in the same language and uses the same license as Muine, so it should be easy to port if deemed useful.

[1] http://www.o-hand.com/~iain/last-exit/index.html
[2] http://www.o-hand.com/~iain/last-exit/last-exit-2.0.tar.bz2