Conquerors of NaNo, explain yourselves! (Please.)

First of all, congratulations to all of you who completed NaNoWriMo!

NaNo, for the uninitiated, is a challenge to write a 50,000-word novel in the month of November. It's a really cool idea, and obviously, it assumes that most writers will leave revisions for December and beyond and just focus on getting words onto the page. That, I understand.

What's harder for me to wrap my mind around is where planning fits in. Even if I go into a project with a good idea of what's going to happen, I find that the first few chapters are the slowest going. At that point (and I've heard other writers say this as well) every line involves decisions that will affect the rest of the novel - what kind of character is the person who's about to say something, even a basic something? How does the narrator feel about every person and concept that comes to his or her attention? Once I get past these questions, I can produce volume faster, but in order to do NaNo, I think I'd need to spend October producing thirty pages and an outline.

So, NaNo champions, I'm curious - how do you do it? Do you do lots of planning before the month begins? Do you jump in and make notes as you go if you change your mind about major plot elements or character traits? Do you make a rule that doubts have to shut up until December?

I'm impressed, guys. And very curious.