Just a day after iOS 6's unveiling at WWDC, it was jailbroken by the iPhone Dev Blog team.
MuscleNerd, part of the iPhone Dev Blog team, showed off the jailbreak on his Twitter, stating, "Here's ioreg of my tethered-JB ipt4g 6.0: http://is.gd/1qOwvW ..MANY things including Cydia are broken, don't expect beta JB for a while!"
Considering that he managed to jailbreak iOS 6 in 24 hours, I think he should be given a little leeway in not getting Cydia, which simplifies the jailbreaking process, to work just yet.
His Twitter feed also revealed some good news for iPhone 3GS users. There's a possibility that the jailbreak will restore full GPS functionality to 3GS users, as baseband 06.15 removed the ability for 3GS users to use their GPS, so the GPS fix of downgrading from BB 06.15 will no longer be necessary.