w00t is the Merriam-Webster's Word of the Year, a slightly less prestigious award than the Wordie Word of the Year . Now, my first reaction was WTF, is this from 5 years ago? This is an old word, and if it has increased in popularity, I haven't heard it. I guess it has gotten popular among the kids, which is funny, because years ago it was popular among the kids who are know my age or a bit older.
I have read several etymological theories for the phrase, but none were particularly convincing. Given it's status as an internet word, one should be able to trace the first usage, to USENET, a bbs, somewhere.