In this blog post, Cory Foy discusses how to apply the Pareto law, the famous 80/20 rule, to the concept of minimal viable product. He defines two starting positions: you have to sell a solution for a problem or there is an actual need in a market. A Standish research shows that 45% of the features of a product are never used. This are the features you should not create if you want to deliver your product quickly.
The key definition of Minimal Viable Products is that you know the highest value features, so you build and ship those first. Incremental releases allow gaining experience to improve the product. If you are filling a void in a market, he jokes that you should create initially a product with unwanted features, because when customers are irritated, you will learn quicker.