Despite iOS 5 incorporating a number of features that made jailbreaking the iPhone so attractive, the jailbreak community remains alive and well, and more importantly, committed.
Within 24 hours of its debut, iOS 5 has already been jailbroken.
According to iOS hacker MuscleNerd, the exploit uses limera1n and is a tethered boot on the iPod touch fourth generation at this time. Cydia installs fine and seems to work without issue.
So while, yes, iOS 5 has been jailbroken, you have to have your iOS device connected to a computer on every reboot. As it stands now, iOS 5 is only available to developers and is on track for an official release sometime this Fall.