Clearly depicted in the pic is a modified version of iBoot, which means he has somehow bypassed the sig check on the iBoot 596.24, which is the new one for the 3GS. The project he seems to be working on is what he calls "Purplera1n" or "purple rain" instead. He's even put up the site for it at http://purplera1n.com/ though all it sports is a pic of him with the phone, getting wet in purple rain . . .
However, as said by some other big names like posixninja, this is an exploit which could be built into a Tethered Jailbreak and is not even sure if it will ever get developed into a full fledged "Jailbreak" due to the obstacles involved.
iZsh: my guess: heís just playing around, I donít think heíll do a full jailbreak.
We do hope there's a working jailbreak based on it out soon for our 3GS folks!
[iPhonejtag and iPhonePulse]