I've seen the work of MonsterMedia, which uses a projector and motion detection to create eye-catching advets in public areas. (you walk across an image on the floor and it ripples where you step).
After speaking to them, they aren't in a position to turn their software to different things yet, and I'm hoping to create giant, floor quizzes at my school. The sort of thing I imagine is a question on the floor and multiple choice buttons you step on.
I've been playing today and began to get some promising results, but I wondered if anyone here had any experience they could to share and any advice I could get to avoid certain pitfalls.