We've seen Sprint, AT&T, and T-Mobile release their variant of the Galaxy S III so far, and all three have been rooted. Nobody really expected it to take very long, but it's still nice to know it is done, and the devices are now ready to reach their maximum potential.
Of course, you don't have to root your phone, and we don't blame you if you take a pass. The methods aren't abnormally difficult or different, but they're a bit more complicated than simply clicking a button. Then there's that pesky issue of voiding your warranty to think about. It's something to consider before you jump in. If you're ready to give it a go, the links are below.