Do a bit of a search about AI Servo versus AI Focus. My understanding is that AI Focus allows the camera to choose if it thinks Single Shot or AI Servo is required. If you know you're going to have a moving subject, take control yourself and set AI Servo. If you know your subject will be still, use Single Shot. That's the common recommendation on POTN, and I've had better results with it too. One of many threads on it:
http://photography-on-the.net/forum/...d.php?t=145826
Yes, there's a lot of snapshots there. You have to filter through them for innovative and interesting shots.