I guessed it was a big pain in the arse, and this article at Slate.com confirmed this. And if you’re thinking, “oh more reading? I hate reading!” Well it’s relatively short, and easy to understand even if you’ve never laid in bed thinking about this before (“laid” or “lied”?).
It brings up an excellent point at the end, why would any filmmaker convert from 2D to 3D in post production instead of just duct-taping a second camera to the first. The post-method requires dozens of artists to go slightly crazy 30 times per second as they have to separate elements of the movie into layers, and occasionally fill in some of the separation gaps. The duct-tape method requires some guy named Jim to hit the Record button on two cameras at exactly the same time. Seems to me with ALL the money that goes into a big budget movie, having a second camera rolling right next to the first one, wouldn’t even be something you would do for 3D necessarily, its just a good Plan B.
Well, what do I know. I still check my 3D glasses for a red and blue tint.