Cold Weather...
Frozen Lake...
4 Wheel Drive..

Think of the possibilities (you were expecting a stupid priceless ending werent you).

A bunch of Ronin Guys hit the races here is a vid of it.
http://web.mac.com/nissanclay/iWeb/Site/Ice%20Racing.html

That looks like fun..

awesome.

Who decides when/if the ice is safe to drive on? Anyone ever fall through?

For the ice races that we usually go to, the city checks the ice thickness and then gives the club that runs the races the go ahead.
I'm sure someone has dropped a tire into a hole in the thinner ice before but no first hand knowledge of it. A couple years ago it was warm enough that the ice was only a couple inches thick near the bank and it made for an interesting time getting on and off the ice