Sean Lindsay publishes a blog titled 101 Reasons to Stop Writing. In a recent article, he provided a comparision between National Novel Writing Month and the so called "pulp" novelists. Authors like Wallace, L'Amour, Faust, and Creasey turned out hundreds of novels in their careers. According to Lindsay's article, they most likely didn't even produce a second draft of their work, and thus, the reason "pulp" writing ultimately declined.
The general theme of the article is that a novel written in a month probably isn't good enough to be published. The last sentence pretty much sums it all up:
"Which leaves your clumsy, meandering, plotless, padded, first draft, 50,000 word, 30-day novel only two places to go: your bin, or someone else’s."
And if that's not enough motivation for you, here's another article from the website specifically addressing the NaNoWriMo experience. Click here to read it.
I'm not quite sure whether the goal of the website is to "spoof" NaNoWriMo, or if Mr. Lindsay wants to be taken seriously. I hope it's the former.