The full game ships with four wireless buzzer controllers for chiming in with your answers, which has led some people to conclude it's a simple rip-off of the PlayStation 2's wildly popular Buzz series, but empirical evidence suggests Sony didn't actually invent quiz-show buzzers, so they're probably all right.
As for the demo, it's 619MB and that's about all we know from staring curiously at the Xbox Live Marketplace screen. Perhaps you could try it and then use the experience to help decide whether you like it enough to spend money on it. You can also read our first impressions from E3 to help make up your mind about what's on offer.
Look out for a review of Scene It? Lights, Camera, Action a) closer to release, b) providing we can get through more than half a dozen games without a fight breaking out, c) if we can be bothered to leave the pub early enough, d) all of the above.