Woot is a term to denote excitement! According to the Online Slang Dictionary it is "used online mainly as an expression of joy." Another source said that it was mainly used by hackers. Now, I am no hacker--and would contend that I picked it up from Teen Girl Squad--which I think is the real source of the term.
Now Teen Girl Squad--it is a hysterical parody of teen girls from the site HomeStarRunner. My roommate and I used to watch it in college all the time. Some of our favorite ways to acknowledge our moments of blatant shallowness come from the cartoon:
"Let's get cute!"
"I have a crush on every boy"
"Let's get ready to look soooo good"
"Msg'd!" "Ow! My stomach lining!"
"So good or no good?"