The exploit is not new, it was refined from previously discovered code. The scary new development is that it doesn't require user intervention, i.e. clicking on a button, just loading a Web page containing the malicious code will lock up your iPhone.
The vulnerability is confirmed to crash iPhone firmware 1.1.4 but we're sure about older firmware versions. When I clicked on the link on my 1.1.4, non-jailbroken iPhone it opened a new browser window and the "loading" indicator in the top menu bar spun about three times and my iPhone locked up tighter than a drum. The spinner stopped spinning and my iPhone became completely unresponsive, forcing a reboot.
I also tested the code with Webkit v.3.0.4 and Safari 3 public beta and it crashed both with flying colors.
The Safari exploit source code is and a link to a test page is posted on iPhoneWorld. You have been warned!