Case in point, it is expected that in the very near future Warner Brothers will announce that both Clash of the Titans and Harry Potter and the Deathly Hollows will go under the post-production scalpel for a 3D face lift. The studio has been openly debating the Clash conversion for a while, but The Hollywood Reporter now tells us that they've loved the tests they've done on certain scenes and have now bumped the film's release date to April 2nd to accommodate the change. And, in fairness, this seems reasonable on WB's part as Clash isn't going to be a guaranteed hit, so it makes sense they'd try to hedge their box office bet.
Harry Potter, on the other hand, is a more blatant case of milking the audience for as much as possible. Being the final film(s) of one of the most popular book and film series ever produced, it's safe to say that the audiences were already going to flood the theaters on November 19th. Now we will all just have to pay an extra 15-30% more for the privilege to do so despite the fact that neither film was shot with 3D in mind. Thanks, Avatar!