Farecast became useful to the majority of the country by increasing to 57 airports from 2. Their distinguishing feature is their prediction engine which is supposed to tell you how the lowest price of your search is going to go. Ideally, they would be able to tell you when you are buying too soon. Secondarily, if you are not sure you want the trip, they can tell you if you have more time to consider, or if the price is about to skyrocket. This information is conveyed after search with an arrow:
I have done about 5 searches, and have not seen a time when they expect the price to go down. This is not too surprising because that would generally mean the airline has performed its own poor prediction.
An interesting side note is that “Farecast seems determined to have an amiable relationship with airlines and it will be interesting to see if they succeed.” from techcrunch‘s second coverage. Finally, the search results page is very clean and ajaxy which might have made this my new favorite travel website even without the cool technology. See the coverage.