For me, quite apart from the idea of the challenge it is a good chance to write in a different genre and play around with ideas; in the same way that training in the swimming pool can make you a better runner.
It is a lot of words and not a lot of time. The challenge (as you would expect) has its own website complete with forums for support and advice and the ability to upload word counts as the month goes on (http://nanowrimo.org). It is for writers the equivalent of doing a marathon or an ocean crossing.
So it’s notebooks, computers and sharpened pencils at the ready for the 1st November and see what can be created.