It appears that this is enabled recently. The first mouse click on any hyperlink on a stack exchange site always redirect to
Personally I find this extremely annoying. It has never been this way since Stack Overflow started. The on-click ad behavior gives me a very negative impression of the Stack Exchange network. In fact, it encourages me to visit less often, which means less new questions and less answers.
Worse still, every stack exchange site on the network counts as a new site. So, if I visit SuperUser and get the ad, then visit ServerFault later, I will still get the ad on the first click.
Please turn off this feature......you are driving users away, literally.