The Hat Puzzle

Here's a great puzzle a friend of mine challenged me with. Post a solution to the comments before I post tomorrow! You can find another version of this puzzle at: http://en.wikipedia.org/wiki/Hat_puzzle

Say there are 10 prisoners who will all be lined up facing forward by the prison warden.

They will each be given a black or white hat to wear... something like BWBWBBBWWW.

Since they are all facing forward, all they can see is the prisoners in front of them.

The game is this: Starting at the back of the line, each prisoner must say "black" or "white" and that is all. If a prisoner is correct about their own hat color, then they live. If not, the warden shoots them.

Before this begins, all he prisoners may get together and discuss a strategy, but the warden is listening in.

How many prisoners can be saved?