Chris Anderson has an interesting article about the massive parallel culture on the Internet in the context of the Long Tail. He posted the picture Anil wearing the Goatse t-shirt in the New York Times interview as an example. I was looking at the list and one that I had somehow missed was "More Cowbell". (It's sort of the opposite of stealth disco.) Thanks to Google, I was able to find a video of the original skit. (The link to the mp3 on The Cowbell Project page was broken.)
The Contagious Media Showdown targets this genre, but I wonder what it is that ends up becoming a pandemic in its virality. I guess it's something that is sort of stupid, but gets funnier and funnier the more you repeat it.
I think that the "shared culture" aspect of it is important. It has to be simple (stupid) enough so that almost anyone will think it's funny or at least silly. I notice this with topics on blogs as well. Deep and well researched posts will often receive thoughtful comments, but it's the short 3-paragraph form that seems to consistently be the most read and linked. I don't think it's necessarily a good trend, but it's sort of the blog version of the TV sound-bite - the attention-span of the average blog reader.
I know that a lot of people sit around and think about memes a lot so I may be treading old ground, but I think it's interesting that non-geeks are getting sucked in and these shared ideas create some sort of community bonding that moves faster and at a larger scale than in the past, but still remains nichey and obscure...
UPDATE: Noticed the Wikipedia Cowbell entry has a reference to this skit.