Back when the somewhat scatalogical student production "Easy Mac Death Metal" had 22 hits, I predicted it would do well.
It has. In one month, it has nearly 2,000 views. Now, we can argue over whether that's successful for a YouTube video or not, but it's significantly more views than the high-priced The Undergraduate video by The University of Florida has gotten in over eight months. And this is a video shot in 10 minutes with no marketing or promotion of any kind.
Why does it work? Just look at the title. It taps into broad pop culture themes.
When I found Easy Mac Death Metal, I posted it to a music mailing list I'm on. It's a small list, but it easily reached 40 people. And those 40 people are all different ages, with different social networks: it seeded into a dozen other networks.
I'll say it again: the secret with viral video is your prime audience is not your targets, but your carriers. (And I apologize for that sounding so marketing-like, but it's true). Figure out what people will enjoy receiving, and then work from there. If something is truly viral, what you're selling will be irrelevant to 99% of the people that forward the video. Repect them and keep that out of their way.