It's great - sooo worth it if you can spare the time to write approximately 1667 words a day. Definitely a lot of work, but I think it's a great writing exercise. The goal is quantity, not quality, so anything goes - and you get the bonus bragging rights of saying "I wrote a novel in one month"!
As well, for anyone who wants to try it, I'd recommend getting involved with the NaNo forums or with your other Nanoers in your area. They're probably (from my experience, at least) an amazing, crazy, nerdy group of people and getting involved is definitely motivational.
tl;dr - NaNoWriMo is awesome and you should give it a try.