A big virus
Emphasis on the big part. Hummer Parody.
I think the interesting part is an ordinarily staid non-profit can find a way to interact with a large number of people by doing something that seems risky. Of course, it's a safe strategy, compared to buying yet another ad, anyway.
Worth clicking through to the Experiment, the agency that built the site. A little too much self-reflection on the site, but also a neat way to look at how the death of advertising is changing the very agencies that make it.