I tried NaNoWriMo in 2005, and I was pretty into it for about a week, and then I stopped dead on the story and never opened it again. I ended up deleting it from my computer LOL. But I did write a lot in a week, and it was a nice little break from BMS, and it reenergized me to go back to BMS.
I haven't tried it since, but I do think it's a nice idea for people who either have a hard time updating things and need to challenge themselves to write every day, or for people who stop to think about every word they write and keep rewording things until they sound just right (that is me these days).
If I had an idea for a quickie that I could just write and write on, I would probably try it again, but I always forget about it until it IS November, and then I have no idea, and so I don't do it. And honestly, any idea that I find worthy of writing, I don't want to "waste" on NaNoWriMo because I want to do a good job with it... and that means taking my time, working on it when I feel inspired, and writing it well the first time... because if I write it quickly and poorly the first time, there won't be a second time because I don't like to rewrite.
If you decide to participate, good luck with it!