I highly doubt they really sat down at a table and went "Alright guys, we've gotta convert more people to our cause, how's an ad on the side of a bus sound?" I think it's much more probable that the ad is more of an image-builder than anything. To me, the ad basically says "Why worry about a higher power, just be happy anyway". I think many people view atheists as angry, baby-eating, evil people. This ad puts them in a more positive light by saying that atheists are just like anyone else...all they want to do is enjoy their lives. Also, this is a bit off-topic, but am I the only one who seems to notice more pissed off, unhappy Christians ranting about their beliefs than pissed off, unhappy atheists/agnostics ranting about theirs? Christians need to lighten the hell up. (no pun intended)