I have found it highly variable, ranging from indifferent to effective. IMHO "Megamind" made the best use of it.
But movies filmed would probably have to be refilmed with 3D cameras. I'm sure they could be reprocessed as well, but that would require a LOT of work to be done right.
Done for the sake of 3-D alone, it wouldn't be worthwhile.
But a script rewrite, as is typically done, might be okay.
The ultimate transition will be to what I call holographic; it means that the action can not only be seen in 3-D, but that you can change your viewpoint as well.
This would mean that every item in the "film" would have to be identified in the database, just as we have adjustable type fonts. This would require enormous memory storage capacity, but it would also mean that "refilming" could be done at any time, with relatively straightforward computer operations.
Eventually, you'll be able to put your own faces into your favorite films, do your own voice-overs, and so forth.
The only thing beyond that is a voice-controlled computer system that can mix up a movie to your specifications on the fly. Just tell Robbie the Robot what you want to see.