Worst spill: actually happened on a road bike, slipped on sand while turning and slid 10ft while clipped and ended up under a stopped car at a street light. luckily the light was red
Yea it happens.... rarely with mountain bikes with suspension though. I used to see it allot more often while racing Bmx.
That is the most common place for a frame to snap due do all sorts of pressure. Most of the time its due to a bad weld thats holding it together up there.
Ha as for the worst crash i would have to say being taken over the last turn at this race and had like a ten foot fall to concrete...not so fun.