JackProton wrote in post #3689028
The XTi and 30D use this same focusing system I'm told.
You've been told correctly.... however the thread is about the 350D aka Digital Rebel XT. The XTi has a totally different AF system, mostly borrowed from the 30D.
Going back to the OP's question, I've recently upgraded from an XT (now my backup body) to a 30D after shooting a number of motorsports events -probably the toughest test of a camera's AF system- and the two main improvements for me was the AF accuracy and the faster drive mode (5fps vs. 3). I've had a much higher keeper rate, and getting a racecar in sharp focus with the 30D isn't nearly as torturous as it was with the XT.
Actually, it's almost fun.
So really, the 30D's improvement in AF speed and accuracy will really become apparent in a demanding, fast-action environment. If that's the type of thing you shoot, the upgrade will be worth it.