I use both as well, but it's like 95% mouse / 5% trackpad, if that. And I'm definitely not a fan of the Magic Mouse. It's too low for me and too heavy, and because I rest my hand on the thing, I always end up having to work extra hard to not touch the button areas with my fingers. I've tried going 100% trackpad but it just ends up feeling rather fatiguing and not very precise for graphic design work.
(After much switching, I think I found my endgame mouse, which is a
Logitech wireless gaming mouse that just came out.. I've used however many dozens of mice over the years and this thing blows them all away. I'm not a gamer, but holy crap is this thing quick and accurate. It's a whole 'nother world.)