Trackpad works great for me so far. I almost took it back when I first bought it as it just seemed a little alien to me and then decided to give myself a little more time with it. At first I enabled the tap mode for button press but that became a pain and I was constantly opening or doing things by accident.
I turned off the tap mode and went back to the default mode where you have to physically push the trackpad for a button press and that is working fine. It's easier to press along the bottom edge so I scroll now with my finger and use my thumb for a button press at the bottom edge. Pressing down with two fingers gives you a right button click.
Now that I'm used to the thing, it's a keeper. I was having some mild wrist pain on and off from my mouse and using the trackpad has eliminated that. As someone else already mentioned, it won't totally replace a mouse but I'm now at about 90% trackpad use and 10% mouse. Using both breaks up the stress on my wrist and I'm happy. Being able to use the gestures on the trackpad like "pinch zoom", etc. has become indispensable to me. Cheers!
P.S. I'm using a Microsoft bluetooth mouse as my second input device, not a Magic Mouse. I have a Magic Mouse that came with my iMac but I hate the thing. It's uncomfortable to hold and the acceleration algorithms are awful compared to the Microsoft Mouse or the Trackpad. The Magic Mouse even maxed out on acceleration settings is unbearably slow and tedious to move across a 27" screen, at least for me. Not sure why they can get this right on the Trackpad and not on the Magic Mouse.
James