With iOS 6, Apple want to fight back against the jailbreakers. It's reported that iOS 6 has closed numerous security vulnerabilities found on previous version. Among these fixed vulnerabilities, there might be some vulnerabilities used by the jailbreakers to exploit iOS and able to bypass it's system to deploy the jailbreak.
Jailbreakers has said to stay away from iOS 6 unless you know the risk. While some has reported that a tethered jailbreak has already being done in iOS 6, most people will definitely wait for untethered jailbreak and that will not come in short time.
We will have to wait until the official announcement from the jailbreakears :)