Verizon’s method of pre-ordering is quite different from other retailers. If you pre-order a device, you purchase it and extend your contract without actually getting the phone. You may look down on it, but it comes with its up sides. First of all, it means your contract will end sooner, and you don’t have to wait for the phone to start a new contract.
Another perk is being able to choose a data plan before it disappears. By the time the Galaxy SIII comes out, unlimited data on Verizon will be a thing of the past. If you get it now, you’ll grandfather yourself into an unlimited data plan until the next time you upgrade (which will be in a minimum of two years). You might want to look into that if you’re a heavy data user.