I have just discovered the Magic Mouse touchpad feature. It feels kinda useless right now, but it would be great if we could use it in horizontal orientation. This would give more room for tracking and gestures. Would also be amazing if we could change the tracking speed.
The tracking capabilities of this are really limited, back then the idea behind it was to use it as a powerpoint remote. I don't think it makes a lot of sense to use this for much else, it's not even possible to turn off the cursor movement for the Magic Mouse.