I think the frames themselves are usually ok after a crash, but its things like steerer tubes, handle bars, stems, rims (
) that take more of the brunt. Having touched upon structural engineering in my degree, this makes sense, as there are a lot of places that hit the ground before the frame. And the steerer tube is particularly vulnerable due to the torsional forces that can be imposed on it as a wheel held by a fork say want to go one way and the bars want to go the other. The steerer tubes are designed to take a vertial load more that lateral.
Having said that Dan Duguid did actaully write off a carbon specialised frame yesterday at Dunsfold in the 1/2/3 3Day. Apparently the top tube, and the down tube both snapped, and upon later inspection the chainstays were mashed as well. Mind you, he was a lil cut up too. He finished however, on a borrowed bike, to maintain his second spot on GC and Points lead. What a legend.
Of course being sponsored by sigma, i believe he turned up on a shiny new one this afternoon!