iPhone Alley is reporting that updated USB kernel extensions in yesterday's Mac OS 10.5.6 update breaks mac-based iPhone/iPod touch jailbreaking tools. Workarounds are documented by the Dev-Team blog and include re-installing the relevant 10.5.5 kernel extensions or using a USB hub.
While many may have lost interest in "jailbreaking" their iPhones since Apple has implemented the App Store, the Dev-Team has been responsible for software unlocks of the original iPhone and is working on a software unlock for the iPhone 3G.