VeloNews had this come up a while back:

http://www.velonews.com/article/71286

As for clipless pedal usage, just remember my two rules:

1) Anticipate your stops. Don't wait until you are at the stop sign to come out of the pedals. Physics doesn't stop just because you aren't clipped in, so just put your foot on the pedal and keep turning the cranks if you need to, which is helpful for rule #2:

2) Don't try to clip in after you get going from a stop until you are going fast enough to coast for a long way. Most people try to clip in, can't, and lose momentum and have a zero-speed fall. Just put your foot on the pedal, and get going. Most of the time your foot will clip in on it's own. If not, you can get some speed built up, then worry about clipping in later.