My foot has slipped off the pedal in wet conditions a couple of times, once causing me to lose control and wipe out in the middle of a busy street. So I ride with clips now for safety. I also really like being able to draw my foot upwards at a stop and have the pedal go with it. I, for one, don't really care about the supposed speed benefits.
The safety downside is that if I do go down, I'm going with my bike, and it'd be difficult to maneuver away from it. My dad's been in accidents where he and his bike were on the street and he literally rolled over towards the parking lane to avoid getting hit while his bike got caught under a car. But for the type of accident I seem to be prone to, clips make sense.