"Superboot is a boot.img that when flashed, will root your device the first time you boot (installing su and the superuser APK). No need to flash the system partition, no need to use ADB, no messing with the contents of your data partition, no overwriting the shipped ROM on your device, just flash the boot image using the instructions below and you're done!"
- Download the zip file and extract
- Connect Nexus S via USB cable (with debugging enabled - Settings->Applications->Development->Check "USB Debuggging")
- Boot into bootloader mode - (Turn on while holding 'volume up')
- WINDOWS - double click 'install-superboot-windows.bat'
- MAC - Open a terminal window to the directory containing the files, and type 'chmod +x install-superboot-mac.sh' followed by './install-superboot-mac.sh'
- LINUX - Open a terminal window to the directory containing the files, and type 'chmod +x install-superboot-linux.sh' followed by './install-superboot-linux.sh'
*Again, All credit goes to Paul at Android @ MoDaCo*