There is no possible way I could write an entire novel in a month all by myself. Community has been a key motivator for me. My lovegirl isn't writing a novel with me, but she decided to write an essay every single day (she's really good at personal essay/non-fiction stuff) and that has kept me poking out thousands of words these past two weeks. My friend Estee is also writing a novel this month and every time I see her word count posted on facebook I think, "I better get writing!"
For NaNo there are even regional groups of people who are all participating in NanNo and sometimes they get together to have a write-a-thon. I've never been to one of these, but I do have a cute little community of my own at home who have kept me motivated.