MY daughter has a Nexus S (from Vodafone but now being used in the US with T-Mobile) and it had ICS pused to it. She is telling me that battery life is not good with the phone not lasting the whole day even when inactive. She found some forum where it said if you turned off auto rotate it helped with battery life and it did a bit but the phone still doesn't perform as well as it did with GB.
I have a Galaxy Nexus coming and if the problem is OS related, then I suspect it will manifest itself on that phone also.
For those with the Galaxy Nexus (or who have a Nexus S that has been upgraded to ICS) I would be interested to know what sort of battery life you are getting and if you had problems, what you did to try to fix them.
Thanks