I understand that from an SEO perspective it is beneficial for stack overflow to have the no follow attribute on the website link for user profiles. Especially if people will just create an account to get a backlink.
What I think however, is that contributing members of stack overflow should be awarded with this backlink. I think that if someone contributes and has some decent reputation, then they should not have nofollow set on their website link in their user profile.
Considering the amount of users that are backlinking to stack overflow with flair, I really think that stack overflow should hook us up with some search engine love.