I remember a court case where a website's terms of use precluded search engine bots for indexing the site. The fact that the site owner did not use the industry standard of the nofollow tag ultimately worked against them.
So yes google can disregard nofollow on a case by case basis and face the associated potential legal consequences. I am sure that this would not be a problem in the case of stackoverflow, but I am not sure this is true in general.
So yes google can disregard nofollow on a case by case basis and face the associated potential legal consequences. I am sure that this would not be a problem in the case of stackoverflow, but I am not sure this is true in general.