Google and Bing are free to decide to just disregard 'nofollow' tags on stackoverflow.com if they want.
Remember the tag was only put in place to help search engines in the first place. (Well, to stop people from spamming to get good search engine results. I think you get my point.)
Remember the tag was only put in place to help search engines in the first place. (Well, to stop people from spamming to get good search engine results. I think you get my point.)