iOS 5, at least the beta versions, have been jailbroken literally hours after their public release. Of course, these jailbreak methods were tethered meaning that you’d have to reapply every time you reboot or power cycle your phone.
It appears that an untethered jailbreak solution — the one that is permanent and outlives any device restarts — is currently being developed. According to a tweet by one of the members of the iOS hacking group Chronic-Dev Team, the jailbreak solution is currently in the works. Because of obvious reasons, betas will not get permanent jailbreaks as it would give Apple the information and time to patch things up before the official public release. There still might be hope after rumors of Cupertino trying to patch everything in order to prevent untethered solutions.