A mad mad mad idea where you write a 50,000 word novel in the month of November. If you start at the start, you need to average 1666 words a day, or about 1.15 a minute, over the whole month. I'm currently on 600, thoyugh I have chocolate and am about to get tea to speed me through another writing session.

All the stuff for it is at www.nanowrimo.org