On StackExchange, some people use their real names, while others hide behind a username.
I was wondering, do hiring committees look at a candidate's StackExchange account and consider the candidate's activity on these accounts?
I know committees look at my website, they openly mention this during interviews. They also ask me about things that they would only know about after seeing my website. I have yet to connect my real identity with my StackExchange account, because of my reservations about this.
As Dan Romik said, anyone can look up anything on Google, so a StackExchange account would possibly be looked at. But I would say that this will only occur rarely, if at all. And it certainly would not amount to a formal indication of either acceptance or rejection.
On the other hand, a StackExchange presence is part of one's online presence as a scientist and so may effect your overall scientific presence, prior to ones application for a job. But it will not be a significant part of the hiring process had the hiring committee do not know your stackexchange participation in advance.