One thing I don't like about my Kensington trackball is the scrolling action: it's is jerky compared to the built in trackpad of my MBPr, other than that I like the trackball. I think I am going to get a Magic Trackpad. I assume the feel of the external trackpad is similar to the built in one on the laptop. If that is the case, it's strange that the Magic Mouse doesn't scroll smoothly.