I'm not participating. I tried to in the past, but it didn't work out. I put up respectable numbers (28,000) but had to do so much revision that I might as well not have bothered.
The about page on the NaNoWriMo website says:
Because of the limited writing window, the ONLY thing that matters in NaNoWriMo is output. It's all about quantity, not quality. The kamikaze approach forces you to lower your expectations, take risks, and write on the fly.
Make no mistake: You will be writing a lot of crap. And that's a good thing. By forcing yourself to write so intensely, you are giving yourself permission to make mistakes. To forgo the endless tweaking and editing and just create.
That's pretty much the opposite way I write. I believe in getting the chapter/scene/paragraph the best it can be before I move on. I don't like plowing through a novel if I know the previous scenes aren't strong. If you fix an earlier scene, it has impacts throughout the book.
Even then, my work needs to be proofread, critiqued, and edited before it's polished enough to let anyone read it. You can imagine what this process is like if you start with word-vomited crap. It's just not worth it.
The other aspect of NaNoWriMo is that it teaches writers to set goals and work toward them. Well, I don't really have deadlines so this isn't a problem. I find that I want to write everyday, especially if I think what I'm writing is good. I don't set a daily goal because I never know what my day will be like. I open my manuscript, read the last scene, continue where it left off, and stop when I draw a blank. I can usually crank out a few hundred words with this method.
But NaNoWriMo requires a lot more than a few hundred words five days a week. For each of the 30 days in November, you have to crank out 1667 words. Keep in mind there's Thanksgiving too. My average speed is 500 words every hour, mainly because I sit there and ponder each sentence, each character action. So to do 1667+ words daily, that's over 3 hours of writing. Between work, family stuff, and the dog that's damn hard to do. It's giving up everything that helps me relax - watching tv and reading a good book.
I feel like the basis of NaNoWriMo is misleading. "It's all about quantity, not quality." I think you'd be better off writing quality work from the start, and with practice, get faster and set goals. Even so, I wish all the participants good luck and happy writing.