The Magic Trackpad really behaves somewhat peculiar: In my case, and used with MS Word, there is a somewhat peculiar "delay" in the response! When I, for example, activate a word with the trackpad. and then delete it by pressing the delete-buttom (back-step) on the keyboard, I have to press the buttom twise before anything happens! Sometimes moving the cursor to another place in the text will cause the same problem, e.g. the new text written, will suddenly appear in the wrong place!
N.B: This does not happen whern using the Magic mouse or the Mighty mouse! (I use either of them when charging the batteries in the Trackpad).
I have had this problem all from the beginning. I got my iMac 21,5!" (i7 processor) in september 2011, and it is continually uppdated. I have hoped the new updates or the new system (10.8) would cure the problem, bu it is still there!
I can live with it, though, even if it is al little bit annoying!