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Dave, the T1i autofocus is very similar to that of the 5Dmk II which makes it a bit slow when used on AI Servo (continuous) I find an object that you are tracking the front of will end up keeping the back of it in focus. This happened to my when i was doing horse photography, I'd always get the hind quarters even though i was focused on the eyeball.
The 7D is so much faster, and you can change the speed of the AI servo for your needs on a sub menu, very handy, I haven't tryed it yet, however, i just learned to pre-focus and stop down the F stop to keep more in focus. I do that a bit when i'm shooting birds. I focus on the eye and stop down the F a little bit so that i have some freedom of movement. Mind you, i can't stand still long enough yet to catch many birds taking off. My attention span is a little short. Lots of learning still to do, but i like the larger window of opportunity to hit my target untill i can develop better habbits and methods.
Mark, if you do get to the point where you're ready to spend on the 70-200, it's a night and day difference over almost every other lens i've touched. it grabs focus faster then any other i've used to this point, which makes it a blast to use on moving targets. It also has a switch to stop it from focusing too close to you, so that if you end up in a hunting focus situation, it will still regain it's focus faster, very handy as well when doing sports and you know objects won't be getting too close.
The 60D also has a faster AF system then the T1i, so that may be a consideration for you one day. but i wouldn't hurry because the T1i is still a decent shooter.
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