Obviously, Stack Overflow is a great tool whether you are just striving to increase your programming skills, or working on a home pet project that's going to turn into the next Twitter, or get free help on your freelance project, or even to find the best solutions to your development problems at your IT job in Corporate America.
However, the downside to S.O. is that you might end up spending countless hours on S.O. during work hours (without even realizing it until it's too late!) trying to boost your "Reputation," and that could mean lost productivity.
Nevertheless, one could still justify trolling S.O. for hours if doing so also helps you solve a problem at work in hours instead of days or minutes instead of hours.
So my question is, do your companies realize that you are spending time on S.O. or ask/answer questions, and if so, how do they feel about it? Of the companies that are aware of the issue, do they impose a daily limit? Encourage/discourage using it during work hours? Does anyone's company go so far as to block the domain on their proxy?
And for extra credit, do you think there is a net increase or decrease in productivity from getting great answers quickly or due to spending too much time on it (respectively) from using S.O? If anyone has any data on this issue, that would be wonderful, but I'm interested in your opinions on this matter too.