I participated last year and won. It was easily the hardest thing I have ever written. The best thing about it though was that I not only was able to finish a 'novel' but it gave me greater perspective on the level of outlining and story planning I need to do to finish something that I could be proud of.
I wrote 4,000 words yesterday, because I didn't write at all thursday and friday due to exhaustion. Today I meant to plant myself in front of my laptop and grind out another 5K, but i've been procrastinating all day. D: