Once they've constructed an entire holodeck, perhaps the point will be moot, but Microsoft Research is presently working on some pretty clever 3D holograms, too. By combining the age-old optical illusion of the mirascope toy with a modern light field display, a team of researchers have managed to make a moving 3D image float in midair at 15 frames per second, emulating 192 different viewpoints at a time.
Typically, such light field displays have to be demonstrated under glass, away from curious fingers, to maintain their effect, but you can reach right out and "touch" these images with the aid of a depth tracking camera like Microsoft's Kinect. The team's calling the project Vermeer, and while the first revision actually use a Kinect mounted elsewhere in the room to monitor hands as they interact with the rays, subsequent prototypes actually put cameras inside the mirascope to detect fingers and capture images to be displayed. We're still a ways away from firing a tiny Princess Leia video out of an astromech droid, but until tiny hologram technologies take hold, we'll take what we can get.