I switch between the trackpad and mouse, depending on my mood and posture. It's good for the hand(s) to switch input devices from time to time, too. (edit: It's a BT MightyMouse)
Have to say, with the UB MBP, I'm tending to use the trackpad more. It's the best I've ever used - the texture they choose for the glass is awesome. It always feels silky, no matter how dry my finger is. Good job, Apple! (I'll take back half a "good job" point for the slightly stiff, noisy integrated button - only a half-point, though, as full surface idea is great.)
(17" UB MBP)