Just six short days after its release, the Nexus S is getting its first over-the-air update, bringing the system to GRH78. The update apparently "contains important bug fixes plus the latest version of Maps."
If you don't feel like waiting for the OTA (and who does?) here's the manual method. Note you'll need to be using the stock recovery image if you want to go this route.
- Download the file from Google right here
- Rename it to update.zip, and place it on the root of your internal storage
- Shut down your phone, and reboot into the bootloader by holding volume up and powering back on
- Use the volume buttons to choose "recovery" from the list, and select it with the power button
- When you see the triangle on your screen, press volume up and power once more and you'll have a list of options, choose to update
Now we get to tear it apart and try to find what has changed, discuss it all in the Nexus S forums. Thanks mojonation1487!