Source: Puzzle Toad, CMU
Problem: Each hat is black or white. The people are standing in a circle. Now our n hat wearing friends are standing in a circle and so everyone can see everybody else's hat. The hats have been assigned randomly and each allocation of hat colors is equally likely. At a certain moment in time each person must simultaneously shout "my hat is black'' or "my hat is white'' or "I haven't a clue''. The team wins a big prize if at least one person gets the color of his hat right and no one gets it wrong (saying "I haven't a clue'' is not getting it wrong). Of course, if anyone gets it wrong, the whole team is eliminated and this is painful. The prize is big enough to risk the pain and so devise a strategy which gives a good chance of success.
Update (29/01/10): Solution: Posted in comments by me.
Update (06/02/10): Previous solution deleted. Solution reposted with more explanation. :)