If certain posters can't calm down and stop getting fanboy trollish because they refuse to accept that not everyone is automatically "YA! They're making another Superman movie! It's gonna be AWESOMEZ!" then take a chill pill and grow up. Preferably in that order.
If it is in fact going to be December 2012 with The Hobbit: An Unexpected Journey, Star Trek 2 and The Man of Steel, my money would be on the Trek sequel as the big winner stateside.
That reboot was incredibly popular with the general public and critics, did $260 million in the US (a huge number all to itself but also when you compare to fellow wildly loved franchise re-starters Batman Begins and Casino Royale) and did something I never thought was possible. It made Star Trek cool. That sequel will be a monster where ever they slot it outside of The Dark Knight Rises.
The Superman franchise is at a crucial stage because of the lawsuits and, in a way, in the same position Trek was before Abrams and his guys took over. This is do or die, baby. If WB could have figured out a solution/direction for the film series, they'd have already done it without handing the keys over to Nolan and letting him do whatever he pleases with it.
You can't just slap on the \S/ logo on one-sheets and flash a Christmas Day 2012 release and say, "Now...it's time to let the money pour in!" They did that on Superman Returns and the grosses fell short of expectations because they, foolishly, didn't think beyond that with general audiences. Again something the Trek people made a point to avoid with their marketing - much to their credit and success.
As for The Hobbit? There is no way Peter Jackson would be running to Facebook as often as he has if these movies were sure-things to do killer business domestically. No matter how popular The Lord of the Rings trilogy was (and boy was it; I love em myself), that was ten years ago. Tastes, trends, etc. change. Like Superman (and Star Trek...and Batman...and James Bond), they're trying to make this series relevant in the eyes of modern movie-goers again. But as we saw with Shrek Forever After and Pirates of the Caribbean: On Stranger Tides, the international numbers on that one will be ginormous. So they're good to go.
Can all three co-exist and all do huge business? Absolutely. As been pointed out, we saw that back in 2009 with Avatar, Sherlock Holmes and Alvin & the Chipmunks 2. But to think they wouldn't chip at one another (since they're all going after the same audience during an extended period of time where a lot of people pay $$$ to go see movies) is crazy.
But...just my $.02 on the matter.