When my momentum is flagging, when my characters seem flat and listless and my plot pointless, I turn to an old standby: the reward. Last year I was actually a bit ahead near the end of Week One, and I promised myself a treat if I could crack 15,000 words by the end of the first weekend. I succeeded, but I think I forgot to buy the reward I had in mind. The ploy, whether it was fulfilled or not, did the trick. I made my self-imposed goal in time.
A mid-stream prize can do wonders for your self-esteem. It doesn't have to be anything grandiose and you don't have to spend a lot of money on it. Take yourself out for a movie (perhaps after NaNo is over). Spend time at a spa. Buy that new technological trinket you've been wanting. I also advocate a treat for winning, as that's the ultimate goal we're chasing here. When I won NaNo one year, I bought my first mp3 player, a cheapie little Sansa Clip, as a reward. It was inexpensive and drove home the point that I'd accomplished a not-insignificant achievement. I've found myself wanting more space, though, so this year I may upgrade in December. Then again, I really would like a starter video camera...
Your reward can be as simple as a day off from whatever mundane chores you may have around the house. You'll probably need the agreement of your housemate(s) for this one, but if you live with nice people, they'll take it in stride, despite the fact you probably chased them off with a broom throughout the month of November. Or you may choose to get ahead one day, promising yourself you don't have to write the next. This choice would be more dangerous for me. I need the momentum I get from writing each day in order to keep going.
If you dangle a carrot out in front of you this November, you may find yourself writing more than you thought.