Chronic Dev Team has just released Mac OS X version of GreenPois0n tool which like the Windows and Linux version can jailbreak iPhone 4, iPhone 3GS, iPod touch 4G / 3G and iPad on iOS 4.1 and iOS 3.2.2 respectively.
Mac version of the guide will be up soon. Stay tuned for that!
Download GreenPois0n for Mac OS X
UPDATE 1: Complete step by step instructions on how to jailbreak iOS 4.1 on iPhone 4, 3GS, iPad and iPod touch 4G / 3G using GreenPois0n for Mac can be found here.