Driving Distances Between Vehicles

Back when I was learning to drive, I went through a computer program for Safe Driving that my Dad had (I believe I did this on a commodore 64...cutting edge stuff at the time!).  One of the things that always stuck with me is the amount of space you leave between you and the car in front of you.  So when the car in front of you passes a sign, then the specified number of seconds should pass before you reach that same sign.  

Good Roads/Weather - 2 to 3 seconds

Rain/Wet Roads - 3 to 4 seconds

Snow/Ice - 4+ seconds

I don't think too many Minnesotans (or possibly Americans) have heard this or if they have they don't seem to care.  It really worries me when you are driving on snowy roads and the car behind you is driving like the roads are in perfect condition (meaning they are about 1 or 2 seconds behind you).  If more people were to live by these guidelines, do you think we would have more car accidents.

Have you ever heard of these guidelines?  How do you determine how close to follow to the car in front of you?