Many jailbreak guides were released for the new iOS 4 firmware running on iPhone 3G and 3GS and iPod Touch few days ago. New version of PwnageTool was released for the jailbreak process in Mac OS X, Sn0wbreeze in Windows, Redsn0w etc.
But none of them were able to jailbreak iOS 4 on iPhone 3GS with new bootrom. But now the problem faced by the iPhone 3GS users having new bootroms to jailbreak iOS 4 on their devices has found to get a solution. The iH8sn0w developers have posted a guide to jailbreak iPhone 3GS iOS 4 with new bootrom.
But this guide is to be followed cautiously and so it is risky that normal iPhone 3GS users try this guide. But anyway if you have lost your patience and is eager to try the jailbroken iOS 4, then you could follow the guide given here to jailbreak iOS 4 on iPhone 3GS with new bootrom.