Several sites have some community promotion ads which have reached the threshold, but the old 2015 ads are still being shown. When will the 2016 ads start being shown?
Community ads for 2016 were not set up on any site till recently, as result of the change to the width of the sidebar. Many community ads needed to be reworked in order to fit the new width and we took the position that we would wait until these were ready before we re-enabled them across the board.
This happened yesterday. We now have 59 sites with a community ad thread on their child-meta - these have all been enabled and the sites should show qualifying ads.
It appears that the new ads were briefly live but aren't now. On the day the stats link was edited into the ad posts five ads on Worldbuilding met the threshold and show a few clicks. At the same time, two ads met the threshold on Mi Yodeya and show a few clicks, but three more ads that later met the threshold have 0 clicks. I'm guessing they were live for a day or so before stopping; whether that was intentional or accidental I do not know.
I'm still seeing the 2015 ads on the several sites.
Edit 2016-03-09 ~01:00 UTC: I'm now seeing 2016 ads on Mi Yodeya and all the ads report a few clicks, which is a change from when I posted this answer.