So I've just completed my renovation of a Gigabrick back to a Gigabeat with Rockbox. So far, these are the things that I really appreciate:
Backlight and disk caching customization. Real batter life-savers.
The ability to actually transfer just mp3s.
Most of all...
Mono to Right channel configuration. I'm deaf in my left ear, and until now, I've always half-hated listening to music on headphones because I'm almost missing something. This is a hugely important feature to me, and I'm really glad you guys had the foresight to include it.
Really liking this so far.