I always use backbutton focus and am very glad I read about it not long after I first got my XSi(so i think its easy to get used to). like many of the others i used it with AF servo. I shot birds in flight, sports, portraits. Funny thing is, I actually didn't know that you needed to tap it for one shot. I've always held it down -didn't realize you could do otherwise! good thing since i mostly shoot action.