This ambient campaign from Publicis Milan is one of those that is probably more effective as a case study than as an actual installation.
McFarland Beer placed heat-sensitive ads inside urinals at a Milan nightclub. Whenever a guy let out a long-enough leak, it revealed a corporate socia responsibility message:
I'm not sure they really needed to focus so much on the stream... or the guy bending down to read it close up. Ew!
Tip (and video) via Ads of The World.