If you buy a 3D HDTV, can you disable the 3D function for 3D films and shows?
Yes. 3D movies that come on Blu-Ray also have a 2D version included. At least... all the ones I've gotten have had this.
My new 54" Plasma has 3D capability. I've tried a few 3D movies just to see how it works. For some things, it's pretty neat. I've got a 3D "tour" of the space station that's really very well done and it looks great in 3D. I think it might work well for sports, too.
But I don't like it for movies-- and I finally figured out why: It ruins otherwise great cinematography. A HUGE element in the way directors and cinematographers set up a shot involves the use, no... ~depends~ on the use of depth-of-field to move the focus front and back in the shot. The whole art of a shot is in moving the point of focus to bring different elements of the composition into and out of sharp focus. The director moves the point of focus to force the viewer to move their eyes according to what he wants the viewer to see at the moment. That's all key to what the director is trying to build into a scene.
But 3D means that the ~whole~ depth of field is ~always~ in sharp focus. What it means is that the viewer is moving their eyes all around the screen. It's physically tiring on the eyes. It makes the shot too "busy" with too many things to look at-- and it spoils the effect that the director was building. It ruins the composition.
It might work well for sports. Football... baseball... any time they could get a 3D camera down into the action it might be a useful thing. But not for movies.