EDIT: This is for GSM Nexus S's, NOT Nexus S 4G. My wife and I each have a GSM Nexus S with T-Mobile.
EDIT 2: See Meisze's post for the link. I'll flash it as soon as it downloads and I'll post some info.
EDIT 2.5: I tried to update but got Status Error 7. I'm going to flash the full 4.0.3 update, then the lite 4.0.4 update and that should work.
EDIT 2.5.5: ok, I get Status Error 7 when i try to flash the full stock 4.0.3 update. I'm going to flash 2.3.6 -> 4.0.3 -> 4.0.4 and see if that works.
EDIT 3: WARNING YOU CAN BRICK YOU'RE PHONE! I bricked mine in the process and just got it working again. I was trying to flash the 4.0.4 lite update and it kept saying Status Error 7. So I restore a backup of the phone from 2.3.6. Without rebooting I then flashed the full 4.0.3 update (ot error 7) and then the lite 4.0.4 (again, no error 7). I reboot and nothing... No Google/lock logo, no recovery, no fastboot nothing. I used Adams tool and get into fastboot. I tried flashing CWM recovery and still nothing.
I fixed it by doing this.
1. Used Adam's toll to get into fastboot. Adam's UnBrickable Resurrector program for Linux http://forum.xda-developers.com/show....php?t=1397393 I used Backtrack 5 (Based on Ubuntu)
2. ran fastboot boot recovery.img (Flashed latest CWM touch recovery 126.96.36.199, renamed to recovery.img)
3. In CWM ran the stock 2.3.6 full update
4. Rebooted and everything was back to normal.
5. Went back into CWM, Flashed stock 4.0.3 full
6. Rebooted, everything still fine...
7. Went back to CWM flashed stock 4.0.4 lite
8. Rebooted and everything is working great.