So I finished NaNoWriMo in 2009. In 2010 I fixed up the manuscript a bit, and sent it to my editors (and to @snazzydee who is my unofficial-but-equally-important editor). I got comments back this week, and am starting to work on revising the book ready for publication next year. And I have A LOT of work to do. Much more than in other books I've written. A lot more broad-brush structural stuff than usual. It's to be expected, after all, I usually write a first draft over six months, not 30 days.
So is it worth doing NaNoWriMo? I don't know. It's certainly more work for my editors. Will it mean more work for me? I'm not sure.
I'll let you know when the book is finished.