ultrasn0w 0.8 has been released today and is now fully working on the 3Gs.
The main 3GS ultrasn0w glitch on hacktivated devices is: need to do Settings->General->Reset->Reset Network settings once.
They have said that stability should be drastically improved for unltrasn0w on the 3GS, for some people however it may take up to 75 seconds after reboot.
To get ultrasn0w 0.8 add http://repo666.ultrasn0w.com/ to your sources.
Sam's Blog 