It's a given that each firmware update for the iPhone and iPod Touch will seal up exploits used by the Dev Team to 'Pwn' the devices, but nobody expected the new MacBooks to present a problem for would-be Jailbreakers. Users over at HowardForums and iPodTouchFans are reporting problems running the Pwnage tool on the new aluminum MacBooks, which don't seem to be able to recognize an iPhone or iPod Touch when it is booted into DFU mode, a vital requirement for jailbreaking.
It's a very specific problem, too the tool still runs, and users who have a pre-modified firmware created on another Mac or Windows machine are able to 'restore' their devices to a jailbroken state without any trouble. It's the creation of modified firmware, which is the central purpose of the Pwnage tool, that has been kneecapped.
Rather then a hardware change it seems more likely that a new build of iTunes, unique to the new MacBooks, is the culprit.
*Normally PwnageTool should detect the iPhone in DFU mode and display this message.