I did it in 2010. Wrote 52,000 words before the deadline was up, but I find that it felt forced. I'd also lined up to write a story with a friend online but got stressed because I was only sleeping 3 hrs a night and trying to get the story out, while looking after a 1year old, and dealing with some heavy stuff personally was just too much.
In March I wrote 56,000 words in week - which flowed much easier, because there was a story in my head that had to come out onto paper.
So I'm not really that interested in doing it again, not unless I had a writing partner... then it would be more fun.
"Always be kind, for everyone is fighting a hard battle." - Plato
Help me, I'm holding on for dear life