A couple of features I can think of off hand:

1) Animation Editor and Flash Tool (will let you make your own boot animations and send them to the player or send someone else's creation).
2) Updating of ID3 tags. I "think" it does this... If you change track titles or whatnot, you can tell Jemplode to also update that info on the mp3. (I remember this being talked about).
3) Updating of HiJack (automatically checks HiJack site for latest version and updates your player) over ethernet.
4) Built-in Logo Editor. Has Tony Fabris Logo Editor built into the program.

I'll let someone else take over from here.