Earlier we had an article about how to invalidate a startup idea. On the other side of the coin, here's a method, with examples (both a failure and a success), of how to validate a startup idea.
Of course your idea is pretty good, and of course you can convince people your features are pretty interesting. But without getting down to brass tacks of pricing and business model, you haven't proven anything about your business.
In other words, once you've figured out that there is some interest in the idea, so that it shouldn't be discarded outright, it is often worth doing a more thorough vetting process to make sure that the product is not only filling a need, but can also fill that need productively.
Jason Cohen tells a detailed story of how, using his vetting process, he rejected one idea and followed up on another. Must-read.