The iPhone Dev Team have stated they can jailbreak the iPhone 3GS right now, but they will not be releasing it just yet as to do so would only benefit a few rather than the many.
The main reason for holding off on pushing out the jailbreak for iPhone OS 3.0 is that Apple will no doubt push out an iPhone OS 3.0.1 very soon, also ultrasn0w needs fixing and they are going to wait to see just what iPhone OS 3.0.1 offers before releasing their jailbreak.
Apparently the iPhone Dev Team are worried that once the jailbreak is out, Apple will fix the iBoot family bug used to accomplish the jailbreak, and will stop signing old iBoots and just sign fixed ones.
