Some stuff I can think of right now:
1. Media player with more features. (Equalizer is a must, both presets and custom)
2. Customizable launcher menu. Creating folders, rearranging icons etc.
3. Auto sort, snap to grid, variable size shortcut icons for the desktop.
4. Able to drag vertical scroll bar instead of "only" kinetic scrolling.
5. Able to control CPU speed. (Auto, 75, 125, 250mhz etc. Extend runtime at cost of speed)