Update: It’s possible with Sn0wBreeze (Windows only).
Recently we learned that iOS 5 Beta 6 can be jailbroken with RednSn0w. Well, that’s what we all thought. Unfortunately, it’s not working as it should, as some jailbreak developers and users have already found.
Some reports from around the internet say that jailbreaking iOS 5 beta 6 with the current version of redsn0w causes the device to enter a boot loop. Be warned, it all seems to work well at first. Users install Cydia, and it seems to function. Then the problems begin.
According to what we’ve read, users experiencing this will have to reinstall iOS 5 beta 6 without the jailbreak for now.