http://www.youtube.com/results?search_query=Hologram
this thread inspired by viewing the very-well-done video footage of Sir Richard Branson (http://www.youtube.com/watch?v=AiCt4fU4E_8), "beaming" onto and off the stage :)
Plus the "Gorillaz" performing live a while ago... cool stuff, apparently pretty simple technique for doing it.