Another thread that will polarise opinion - all the people who only use manual will tell you that you're better off not using autofocus and should learn to focus with your eyes instead, and all the people who only use autofocus will tell you that the facility is there for a reason.
Only joking - although as with all options there are pros and cons. I use both, depending on what I'm doing, and depending on what gives me the best results at the time. I was at an air show on Friday and Saturday, and I used manual focus for some of my shots, ordinary autofocus for some, and the servo autofocus for others - tracking an F-16 as it flies past is way easier with servo autofocus...
Russ.