cycocommute, if the rear wheel gives out, you tend to roll sideways. If the front packs it in, you are usually heading sideways, but slightly forward. Sometimes you are lucky enough to get the bike to take most of the hit. Whenever I've crashed I tend to stick out my arm... even though I know its the worst thing to do.

Luckily in winter I'm going so slow, there is little or no damage. I've fallen 3 times.