MuscleNerd recently Tweeted that iOS 5 beta 1 jailbreak is already available. DevTeam released Redsn0w 0.9.8 b1.
For now the jailbreak is tethered (you have to run redsn0w each time you reboot) and available for Mac OS X only. It will not activate your device, so you need have registered UDID. iPhone 3GS users with 06.15 baseband: redsn0w will get you past the iTunes restore error. This redsn0w will probably work on future versions of iOS 5.
Redsn0w 0.9.8 b1 works with iOS 5 b1 on
This is mostely for developers of Cydia apps. Most tweaks and Cydia applications do not work on iOS 5.
You can download Redsn0w 0.9.8 b1