I tried to have my magic mouse switched out for the trackpad (AKA get a free trackpad). However, they were unwilling to swap them in the store (Rosedale Mall, St Paul, MN for those of you interested) so I've been using the magic mouse. It has been working wonderfully for me doing random stuff on the web and work, however one thing you do miss is the ability to zoom in...actually all multifinger motions for that matter. I'm not bothered by the form of the mouse as I let my hand rest comfortably about the non-ergonomic shape and barely touch it except the sides for movement and top to click. A trackpad in the future will be nice for easy website navigation but the mouse seems fine for now.
Benefit to having both: trackpad for when you're looking at things whether it be pictures, PDFs or website; then the mouse for quickly clicking (right clicking) when working on more serious things like Excel or Word.