Jonah Berger, an assistant professor of marketing at Wharton just wrote a book exploring the reasons why products go viral.
The book, Contagious: Why Things Catch On, covers six key features that all viral products share.
1. Products should have social currency and make their owners feel special
2. Products should have triggers to keep people coming back. At MeetMe, we call this reengagement
3. Your customers will evanglize your products if they have an emotional impact.
4. Cool looking products with high visibility.
5. A truly useful product is often recommended.
6. A good story to tell.
Also visit the companion website Virality Explained.