Just last week we found out that the Samsung Galaxy S III was already rooted. Some devs may have taken things one step further though. There is supposedly now a custom ROM available for the phone before it even gets into retailers hands. Here's a quote with some details,

This newly born ROM is actually created off a former community-collaborated ROM based off Android 4.0.4 build XXALE8 (build as of May 13th, 2012). More importantly, the new ROM is completed deodexed, rooted and zipaligned.
Obviously, this ROM is "untested" at the moment, but it's great to see that things are moving so fast on the new Sammy flagship! Check out the source link for mor info.

Source: TalkAndroid