Plays may use 3D properly in general, but movies don't - and probably won't/can't until a movie can be shown, as others mentioned, on a full hologram stage like a play.
For a 3D movie in 2012, there is only one thing that is being done with it: creating the effect of something coming out at the audience. For the majority of movies, which weren't SHOT in 3D, this is only done for a few scenes, artificially generated digitally, and most of them were contrived to force any justification of the effect at all. Hitting an enemy toward the viewer in a fight scene, throwing an item away or at someone, etc. Having 3D adds absolutely nothing to the film except to the ticket price.
IMO, Avatar was the last movie to actually do it right. All scenes were filmed with 2 cameras to create a real stereo view, all digital effects used the same techniques. A proper 3D movie, like a play, uses the 3D to show depth in the environment, not to show depth coming out at the audience, although a Gallagher concert movie might argue with that statement. We don't need artificial justification to use 3D, and it should not be encouraged unless it adds to the movie.
Pretty sad, really, that the only thing that was learned from Avatar was that 3D makes money. It's become a buzzword in today's movie industry that producers THINK they will make more money with little effort, because the public are sheep, and practically every movie now MUST have a 3D version (in their minds) to be released at all. It doesn't matter to them that the glasses make the movie unwatchable for many, that the movie is too dark to see for most, or that the public complains when they find out that only 20 seconds of a 2 hour film even qualifies as needing the glasses at all. Pay more money and get a worse experience, guaranteed. Personally, I refuse to support this crap with my dollars, and I know I'm not the only one.