StackOverflow is a watershed website. There are very few websites I can go without and StackOverflow is, without a doubt, one of them.

It is difficult to remember the dark ages where every question I typed into Google would link to Expert Exchange and it was a coin flip on whether you'd find your answer.

Very much like GitHub was the tipping point for social coding, StackOverflow was the tipping point for social problem solving about programming.

StackOverflow and GitHub weren't the first websites of their kind but they were the ones that executed it almost flawlessly.