A few days ago we saw the very first factory images for the Nexus S posted by Google. Previously you had to use a community-supplied image to go all the way back to 2.3.4 and then manually flash the updates. It was a pain, and we're glad that Google and the hardware vendors got it all worked out. Earlier today, three more factory images for the Crespo were released, including 4.0.4 Ice Cream Sandwich for the i9020a. Unfortunately, users of some Nexus S models still aren't seeing any ICS love.
The sojuk -- the Korean m200 model -- has a 2.3.6 image available for download, and the Sprint version -- model d720 or sojus -- has the 2.3.7 image available as a "reference only" download. We're not sure what's happening with versions other than the i9020t "world version", but at least the model that works with AT&T is up-to-date.
I still love the Nexus S. I destroyed mine (water damage sucks) and am looking to replace it. Yes, I can use just about any Android phone available and really want my Nexus S back. But it's soon out of warranty, and if you're the type that has to have the latest just root the thing and do it. We've got all the help you would need in the forums, and now with factory restore images you could just roll back and relock it if things go awry.