Out of interest, are there any advantages of using the Magic Trackpad over the built in ones in Apple's laptop range?
They are identical in function. Think of it as a detached laptop trackpad.
I have my MBP on a stand so that the screen is at a better viewing height. This makes the keyboard and trackpad awkward to use. So, I use the Bluetooth keyboard and, now, the Magic Trackpad. It's all about better ergonomics......