I saw The Seven Samurais when I was 2, past midnight, with my parents sleeping. Didn't move me one bit
I actually thought The Blair Witch Project was really scary. I had heard the rumours, but knew they were actors and it was only a movie. But it was just so well done, and I saw it with some friends at night in total darkness. It creeped me out, mainly because the mood was just right I guess.
That's gotta be one of the most perfect ways to market a movie, by the way. Pure brilliance.