Solved!!!! (for me) (Specifically, my Magic Trackpad was not tracking well, was jumpy, slow then fast, moving all over the screen, causing me to miss desired clicks . . .). The problem was also intermittent.
Long story short: it appears to be interference between my WiFi and my Bluetooth (which are currently quite close to each other - 2-3 feet).
I tried shutting down many programs. No go. The mouse was jumpy even at the login page (before even logging in to a given user). No joy from restarts, never got around to PRAM resets, etc because . . .
I noticed some interference between some speakers and the Airport base station I have (I heard very faint noise in the speaker), so I just turned off the base station. My problem with the trackpad was instantly solved.
I think this also explains the intermittent nature of my problem: it was associated ( I guess) with heavy activity over the wireless network, perhaps when the bands used by the protocols overlapped dynamically(?).
This appears to be plausible for 2.4 GHz devices. http://bit.ly/XeUxWp
e-engineers, please correct me where I am wrong/vague.
I hope this helps you. I will be moving the airport base station further away from the computer . . .
regards,
jason
PS- now if only I can get Safari to quit quitting without notice when opening a new tab . . .