yeah, Rusty's correct about the custom led colors in handcent
It's really a handy tool to have when you're somewhere where you have to have phone on silent and "put away" (work), one glance in my desk drawer and I know who is trying to get a hold of me, and the importance (family etc)
Speed and smoothness.
I love a lot of the customization options I have with ADW Ex, (transitions, 4D app drawer, changeable dock icons and re-sizable widgets to name a few)
Being able to change font and font size would be great (I'm moderately vision impaired)
Better on screen keyboard (I still find the one on my iPod touch easiest to use)