20D AI Servo Focus Question

As a relatively new 20D owner, I've only used the AI Servo Function once, with inconclusive results. My Nikon-shooting colleagues tell me that they can use the Nikon version of predictive focus in the following way - focus on a subject somewhere in the frame, which causes the system to maintain focus on that subject, no matter where it goes in the frame. If, from the exit side of a turn, I'm shooting the driver of a racecar with the 20D AI's Servo, can I focus on the driver as the car turns in (car in center focussing zone) and expect that as the car goes through the turn and heads out toward me, the driver will still be in focus if he's (or she's) no longer in the center of the frame? Is the Nikon focus system better than the one on my 20D?
Thanks, Dan