Why I love NaNoWriMo
NaNoWriMo gets you writing. Since the focus is on getting a set number of words, not "perfect prose," you're encouraged to just write and save the editing and self-doubting for later. This is a huge thing for most authors, so any tool to help you do better about getting the words down is a pretty big deal.
NaNoWriMo is for everybody. You can be a published novelist; you can be a fourteen-year-old trying your hand at writing for the first time. Everybody is welcome. I especially like that this applies on the forums, as well. People are busy writing, and the forums are only open part of the year. This leaves less time for any one group of "special" people to take over the forum. Everyone is, literally, welcome!
NaNoWriMo makes November one time of year when it's cool to be a writer. Well, that one's just my opinion, of course. :-) But it's cool to be able to talk about your writing with people who have the same goals and value the same things.