I actually far prefer a trackpad for many activities, especially with the gestures of the macbooks/pros. Reading a PDF, for instance, is much more fluid, as you just swipe three fingers down to go to the next page. Yes, I KNOW there is a page-down button, but it feels much more fluid on the trackpad (you down have to go searching for the button, etc...all the controls are on the same surface). I've actually been looking forward to a product like this for a while.
Just for reference...I [mainly] don't use either a trackpad OR a mouse -- I use a wacom tablet. Much more intuitive (and easier on the hands) than either, except [like I said] for reading PDF's, scrolling webpages, etc -- trackpad is lightyears ahead on convenience there.