Why virality might a real-life application of the least competitive game in the world.
Ars Technica's Casey Johnson wrote a stellar article about game theory being a more apt explanation of viral media than actual virology. The article points out that the epidemiological approach "is fitting for some cases, in others it's an oversimplification—a person's exposure to a trend doesn't always guarantee they will adopt it and pass it on." Essentially, this is the beginning of the explanation for why websites and gadgets succeed, while other, similarly featured ones fail.
The researchers from the AT article ran a couple of models based on game theory principles. The first assumed that likelihood that a new computer application would be adopted by any given person was directly proportional to the number of friends in said person's network that adopted, and that knowledge of friends' adoption or non-adoption was 100%. This doesn't explain much—it creates a world with an infinite barrier to entry, but a preternatural tendency to growth. The second model denied absolute knowledge of friends' choices, and added a "try-it-out" rule: 100% adoption for nodes that had 0% knowledge of friends' tastes.
This was starting to sound a little like Life. Not the cereal, nor the Zen police procedural, but the game. John Conway's Game of Life is a zero-player game. I seriously won't attempt to beat Wikipedia at explaining it (skim it now, then come back), but suffice it to say that outcomes are both: absolutely predictable by machines who know the rules and can compute them on the fly, and terribly unpredictable and surprising to those who don't know or can't, you know, do several hundred computations in a few milliseconds. Patterns that seem small and silly may spread for generations and generations, and intricate designs might collapse in just a few. (Play Life here.)
It's that unpredictable propagation that makes Life interesting. And while the rules of the game are surely different from the much more complex rules of social marketing, it stands to reason that a few things are similar: it's more important who knows about your product/website than how many of them there are to start off with. If people that people trust (read that phrase again) know about your content, so much the better. But if the social networks of your early adopters can serve to propagate your message to other widely-trusted individuals, sounds like you have a really solid start.
There are HUGE amounts of conjecture in this one little post. We of course have no clue what the rules to the idea-passing mechanism are, how to determine who the starters for your viral marketing plan are, or what "special sauce" makes an idea likely to be passed. Memetics has largely failed in this regard; future research is desperately needed here.