I went to see the Light Surgeons a couple of weeks ago at the Coulston Hall in Bristol - really amazing stuff. Documentary meets concert visuals, meets social commentary meets live AV performance. But it was the "live performance" bit that got me thinking. Basically, because the performers were positioned behind one of the two projection screens (it was largely translucent), it was quite difficult to distinguish the nature of their "performance"; what were they actually doing? There was a cellist and a violinist, plus a bunch of laptop performers, and some other folks...but because of the lighting and positional setup, it didn't feel "live" for most of the time.
It's a tricky one this - I know it is. How can a performer make the connection between their actions and the results of their actions sufficiently explicit to ensure that the audience has a sense of "liveness"? Zan Lyons, the support act, had a different approach. He positioned himself in front of the screen and produced some of his sound material on a viola. So it felt more "live"; we could see him, and connect his actions to their results.
Given the very rapid growth of new, more responsive technologies, I think we're going to see and hear a lot more "live" AV performances - that actually feel live. And I'm looking forward to seeing and hearing them.