a quick physics lesson

Alright people, static friction will give you greater traction than sliding friction. Translation, when you're stuck, try to keep your tires from spinning. Spinning your tires in the snow will only increase your likelihood of staying stuck.

I was at the computer a lot today and my window looks out to an intersection with a stop sign on a slight hill. Every so often I will hear and engine rev and tires pealing out only to look out my window to see a car at the stop sign, not moving. I just witnessed a school bus doing this for at least five minutes. He was smokin' those tires! No, literally, there was black smoke everywhere!

This goes for braking as well. Anti-lock brakes were created for this very purpose. When you're breaking on slippery surfaces, you want to apply brake pressure just to the point before your tires start sliding.

There, I hope this helps.