You folks who are asking "What's the point?" and "Why?", citing there is no mouse cursor in iOS:
Folks like me have limited space. The iPad does everything I need it to for business and play. My only computer is a laptop that doesn't come out of its case unless a Windows/iOS update is needed. At my desk, the iPad is docked in a stand that raises and positions it to eye level very much like an LCD monitor and I use the Apple wireless keyboard. While iOS doesn't support a cursor, the Magic Trackpad would give folks a second, more ergonomic way to interact with the iPad while it's docked. Especially with page scrolling, pinch/zoom, etc., maybe some drawing and other stuff. Reaching for the screen to interact with the docked iPad does get old and tiring after a while when you're busy doing a lot of input via the keyboard at a desk. The iPad screen and onscreen keyboard are perfect when I'm using it anywhere else, like when I'm holding it or at a cafe table, etc. Like my keyboard, there's no way I would haul the Magic Trackpad with my iPad but I see a good potential for it at my desk.