This year will be my 7th and I've won every time - since NaNoWriMo sounds a dog whistle to my competitive side and I refuse to not make it!
I've had a couple of not quite as fun years (the less said about 2009 the better. Only sheer bloody minded stubborness got me to 50k on that one.) But now I've done it so often I've got this feeling of having nothing left to prove and can do it for my own purposes (dropping bad habits, restablishing good ones) and for the sheer joy of writing, especially with others. For the last few months I've done a lot of editing and it's been ages since I've done a novel draft, so I feel I have all this pent up drafting energy ready to burst out.
And I'm trying to take it as un-seriously as possible. My novel has a fairly silly working title, I've got a NaNo-ing hat, made playlists, other such NaNo-ish nonsense, just because it's all part of the fun of the event. I still intend to write as good a novel as I can, with the intention of submitting it one day, and when my writing session starts, the silliness stops. But that's fun too!
I get a bit baffled by the people who are having nervous breakdowns about it even before it starts! Hell, if it upsets you that much, don't do it. It's not a homework assingment or a work project your job is resting on. (Writers trying to get something written for a deadline might be an exception to that rule!) There are no serious consequences to failing to get the 50k, so why let it raise your blood pressure that much?