otherwise known as NANOWRIMO
The basics of it is that on November 1st you start writing a novel. On November 30th you stop writing.
You can not edit, doubt yourself, or otherwise stunt or sabotage your success.
Lots of details here:
http://www.nanowrimo.org/en
You can buddy up with pals on the website and share snippits of your work, share your current word count, cheer each other on, etc.
It's fun!
Who is in?