Apple attempts to block jailbreaking by shipping the iPhone 3GS with a new Bootrom that is not vulnerable to the 24kpwn exploit. The iBoot-359.3.2 started to ship last week. A screenshot posted hereshows the new version number.
Now for the time being it would be impossible to jailbreak new iPhones.
MuscleNerd from the iPhone Dev-Team has confirmed that the loss of the 24kpwn exploit would mean a normal jailbreak would be impossible for the time being.