Viral Political Memes - The practice of creating an inherently infectious message or belief

I've been interested in the idea of viral memes since I first read Neal Stevenson's SnowCrash back in high school. Since then I've been on the lookout for examples of them in real life. They have been employed by artists with a suprisingly wide variety of intentions.

ObamaGirl was mostly geared towards entertainment (and likely some ad revenue). Others are inherently more political. Billionaires for Bush is certainly amusing but too easily dismissible. My personal favorite would have to be the Yes Men. I have an enormous amount of respect for their direct action based work. E.g. The way they made Dow Chemical "honest" after the Bhopal disaster. (They impersonated a Dow Chemical spokesperson live on the BBC World News -- publicly vowing to clean up the spill and pay for the medical treatment all those affected. When Dow publicly disavowed the claim their PR shattered).

Just recently I stumbled upon Women For John McCain. Very smart and funny, but I can't help but think that not everyone will realize that it's satire.

What do you think? How subtle is too subtle (to the point where it stops being effective)?