The other thing is that the AF assist light slows things down, and most rides move quickly enough that by the time the AF assist light shines and the camera focuses on it, you've moved on and the AF may not be accurate any more.
On the other hand, continuous AF might be a good idea on the rides. I didn't have my camera set that way last time and I probably should have, now that I think about it...
Also, on the topic of politeness, I think it's a good idea to turn off the LCD review function on your camera, so it's not flashing a big bright picture for a few seconds every time you hit the shutter. I try to be as non-distracting as possible...