I found a site http://www.bookingbuddy.com/ that shows different ads each time you put a different destination (to) city into the for (from: city to: city)

The javascript shows it is getting google AFS (Adsense for search) ads using AJAX, with a result equivalent to doing a Google search for the topic eg. air, shanghai and then scraping the ads.

Perhaps it is a special Google function released on an experimental basis. It gets ads like this:

http://www.smartertravel.com/php/afs.php?w=6&n=0&c=air&q=Shanghai

from javascript like this:

http://slimg.com/js/bookingbuddy.js?v=1.36

Has anyone every heard of such a feature?