Do you use back-button focusing, and why? For anyone who hasn't gotten to the right spot in SDP, back-button focusing is where you bind autofocus to a button on the back of the camera instead of the shutter button. Here's a video of how to do it on the T4i.
Personally, I use back-button focusing so I don't accidentally focus on something in the foreground. When I hand the camera off to someone else, I just switch it back to Automatic Mode, which ignores the back-button setting.