Let’s break this down:
http://www.google.co.uk/url(their tracking and redirect page)
sa=t(“t” for normal search area, “l” for right-hand sponsored results)
ct=res(“res” for normal results, “pro” for sponsored results above normal results)
cd=1(result number for normal results, a unique code for sponsored results)
url=http%3A//www.damieng.com/(the HTTP encoded version of where you were going)
ei=yMf5QoHUJczcQr-YvfAN(a base-64 encoded request number, no doubt tied to what I searched for)
Google’s page then returns a “302 Not Found” and tells your browser that page can be found at https://damieng.com
Google have apparently been doing this on and off for some time.
If you want to see all this for yourself either view the source or try out the excellent Live HTTP Headers extension for Firefox.