“W00t”, a hybrid word of letters and numbers used by gamers and netizens is chosen as Merriam-Webster’s Word of the Year for 2007 via an online poll.
According to Merriam-Webster, the word is used for expressing joy (it could be after a triumph, or for no reason at all); similar in use to the word “yay”.
I don’t use this quite often, but w00t often reminds me of the old steam-powered-train horn… like w00t w00t. I normally used it as a sign of approval for what others are saying in some online discussion boards.