This picture popped up on twitter by @vicjsingh showing us his Nexus S in the update mode. He is on Wind Mobile and he got an OTA so he immediately clicked it and it is Android 4.0 .
To accept the update make sure you charge up your battery, be on stock recovery, and the stock ROM. If you have a Nexus S on Wind check for that update as you’re going to want Android 4.0
Via Android Central