One of the most effective components for creating a successful viral marketing campaign is a valuable offer. When you offer something of significant value (a product, discount etc.) as an incentive for spreading the word (like this viral marketing tool does for generating subscribers) the news will spread quickly.

The fundamental thing that will drive a viral campaign however still rests with the quality of the service or product being offered. Even if a viral campaign is hot initially, it will tank prematurely if customer expectations are not met.