Apple's latest update to OSX, 10.5.6, includes an impressive list of performance and bug fixes but hidden amongst the latest and greatest is that 10.5.6 disables the Pwnage tool, making you unable to jailbreak or unlock your iPhone or iPod Touch with Mac OSX.
The update prevents jailbreaking by disabling the software at the OS level. Apple is stopping 10.5.6 Mac's from recognizing the device in DFU (device firmware update) mode by using new code that affects the USB ports on Apple computers at the driver level and how they interact with the iPhone and iPod Touch.
Apple is constantly caught up in a cat and mouse game with the iPhone dev team, a group that has successfully jailbroken the iPhone and iPod Touch to allow 3rd party applications that are not listed on Apple's official AppStore. At the time of writing the dev team has not commented on Apple's latest trick.