I have been trying for about 3 years now to come up with something interesting I can do with sensor-based instruments as an addition to my regular show. What's difficult about them is that I would like to somehow use them to engage the audience directly in the music-making going on, yet opening up this huge variable has made it difficult to control the form of each piece. Imagine that you've been handed a box with a bunch of sensors all over it during a concert. Well, you start to push buttons to see what they all do. My job is to make the experience clear to the user (in other words, they need to understand right away what each button or slider or whatnot does aurally). My job is also to make the resulting music interesting and cohesive for the rest of the audience. And, my job is to make the whole thing bulletproof, regardless of what the user does.
For me, this task is nearly impossible.
Most often, people remark that they can't really tell what's going on when they interact with the box (because I've made the musical response too subtle, like changing the reverb time or something). So, I figure, in order to make the action have a more clear effect, I need to make the rest of what's going on musically much more sparse. This will probably be what I try next -- more like a duet between me and someone in the audience. Stay tuned.