Paul O Brien of Modaco fame has released a simple root application for Nexus S. Dubbed as Superboot, it spares you of the adb/command lines horrors.
According to the description over at Modaco:
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!
You can find the instructions and download over the Modaco.