A crazy horse-riding dance by Psy and an addictive chorus went a long way towards making Gangnam Style a viral hit, with 2 billion views on YouTube alone.

But there is more. According to analysts, two major factors seemed to contribute the most:

   - Crowd sourcing. The signature dance with simple stomp and arm twirl didn’t come from one or two top choreographers. It was crowd-sourced from multiple dance teams and diverse choreographers. Fun and easy-to-follow ideas that avoided traditional complex dance steps gave it broad appeal
.
   - Open perspective on copyright. The Korean entertainer encouraged parody to expedite diffusion of Gangnam Style via social networking. An “open” policy resulted in a large numbers of parody videos — without concern for copyright lawsuits and resulting in more interest and “stickiness” for the original content.

Via IBM Electronics Blog