They also started advertising in the docs of Capistrano, and when it launched it had a bug that made the ad appear on every pageview: https://twitter.com/kaspergrubbe/status/704355597429436416 :)
I was glad to see open source working allowing someone to see the error and suggest a fix which GitHub pages deployed pretty much instantly... it's nice when a system works!
For whatever it's worth the banner is going away, part of our sponsorship/stewardship of Capistrano now that it's got a bit more manpower behind it is an overhaul of the website and docs, and more guides for getting started more easily for newbies from any tech background.
It was stress built up from converting a plugin from Capistrano 2 to Capistrano 3, and that I had to close that popup on every click.