i don't think it really is a hologram. i read an article somewhere which stated that real holograms (also with a glass screen) aren't possible with good frame rates yet.
it would be awesome if holograms without screens were possible. i read another article a while ago which stated that it theoretically could be possible with very strong crossing lasers that create a glowing plasma or something (i don't remember the details). sounds kind of dangerous though.
edit:
http://www.youtube.com/watch?v=ZeqIZyUMDP4that technology doesn't seem to be very sophisticated yet.
