Yeah, slipping a pedal blows. Doesn't matter what kind of bike either, it just blows. It's also a good way to get a nasty shinner if you don't have shin guards.
This is what I'm poking at, it sucks ass when you slip a pedal. I ride a lot of uphill so having clips or locking shoes is nice because at the bottom of each stroke you get more power since you can actually lift the pedals.
For mostly downhill I think what your going after is better.
PowderHound and TreeNinja