I read about this on TUAW. iPhone Ally is reporting that if you place the iPhone in DFU mode (similar to a restore mode), your iPhone will be unrecognized by a Mac running 10.5.6. From TUAW: "DFU mode is required to jailbreak your iPhone using many of the popular tools such as Pwnage or QuickPwn. So far there is no word from the iPhone Dev group on this finding. In doing our own research, we discovered that the problem does, in fact, exist. So, if you need to jailbreak your iPhone/iPod touch, you might want to hold off on updating your Mac." This is the same problem that is being experienced by new aluminum MacBook and MBP owners that have tried to jailbreak. I didn't see any thread about this, so I thought I'd pass along this info. I know I'll be waiting a little while before I update.