For fiction-writing junkies NaNoWriMo is kind of like New Years Eve to an alcoholic. You know it's dangerous, but it's so much fun, how can you resist? How can you write a good novel in a month? You can't. But you can put down a very detailed outline/rough draft with blazing speed if you're inspired enough or motivated enough. NaNo is a good reminder of that. I get crazy over the need to get the plot line outlined. In some ways I think my best stories are the ones I drafted in only a few weeks of blinding inspiration (both for NaNoWriMo and at other times of the year).
That seems to be how I work best: create some characters and a situation; sketch out the barest arc of an outline; and, then let 'er rip. Let the characters take over. Let the ending surprise me. Drafting is a "Mr. Toad's Wild Ride" for a few weeks.
After that, the story has to lie fallow for a while before I can edit it. I tend to alternate between obsessive drafting (I wrote approximately 20,000 from November 12-14) and very slow editing. In December, I'll turn my attention to editing, not my NaNo novel, but the novel I drafted over the course of a few weeks in the spring.
NaNoWriMo is kind of silly, but it's fun and it keeps me moving forward drafting new stories to work over more carefully later. I'm very happy with this years fledgeling novel, but I'm glad November is over. It's too stressful!