When I got my 50mm f/1.8 I changed over to using only my centre focusing spot as auto-spot just wasn't accurate enough (it usually chooses the thing closest to the camera, more often than not the end of the nose, making the eyes out of focus) and I've never looked back. Now shooting with a 17-55mm f/2.8 and it still comes in handy. It means I have to do a lot more waving around to focus and recompose but it means I get more reliable focus.