I did it the last two years and successfully got to 50k+... I dunno, I found it useful in a sense, but I found that I mostly wrote horrendously long-winded rubbish that would need to be rewritten/edited majorly, and as a consequence both of my novels have sat on my hard drive doing nothing... One of the things I disliked about the whole NaNoWriMo thing was the way some people didn't take it seriously, and wrote 50,000 word association words, or other drivel... which kind of spoils the whole experience a bit.