This problem might cause heated debate, but it's hard to argue against mathematical fact. In fact, to prove disbelievers wrong, I wrote a program to do exactly this:
Three doors, randomly picked one to be correct.
Randomly pick a door.
Randomly choose a door that is incorrect and not picked to be opened.
Switch to the other door and see if it is correct.
The program won 66.7% of the time, after enough trials.
But I have better problems to solve

:
http://www.chiefdelphi.com/forums/sh...ad.php?t=27647
Have fun!