The last two years, I 'won' NaNo (i.e. I wrote 50K words in the month of November) with original fiction - girl-centric fantasy - but never actually finished the stories. They're still just sitting there and I have no overwhelming desire to pick them up again.
I have a third original story on my drive that I've been picking at here and there, and I have a ton of notes and timelines and whatnot written up for it, but I've always read how bad it is to use an established idea for NaNo because of the fear of completely screwing it up. Which is totally me.
When I started thinking about NaNo at the start of the month I generated a germ of an idea... something a little more scifi than fantasy, figuring a change of pace might be a good thing. However, it's still really only a germ. I know a few facts about my MC and her world and that's it. And the idea of going into November with an almost completely-blank slate is... well, I know some people do it, but it's kind of freaking me out.
And then there's always fanfic. I've never done fic for NaNo before, even though it's kosher, because I figured the whole idea was for me to stretch myself. But there's this sequel to White Blank Page lurking in the back of my mind that I'm pretty sure I want to write, and I know from prior experience that I could pound out 50K of Clint/Natasha and Team easy, but... I don't know. It kind of feels like cheating. :\
Oh, by the way, I know it's mostly PMS, but I'm getting ticked off by the commercials for this "Alex Cross" movie. STFU, morons, it's Aaron Cross. JEEZ.