For me the main appeal of Hipmunk's interface is that it makes it easy to use 'soft' search parameters. Every travel agency will let you search for flights bas

For me the main appeal of Hipmunk's interface is that it makes it easy to use 'soft' search parameters. Every travel agency will let you search for flights based on price range, departure time, arrival time, and layover time. However, I usually don't care if a flight leaves at 5 or 4:45, or I'm willing to pay an extra $20 if it means my layover is reduced by an hour. With a normal search interface I'd either have to do multiple searches, or relax the limits of all the parameters and have to sort though a large breadth of results. On top of this, the results are presented in such a way that I need to consider a single variable at a time ("hmm okay this flight leaves a bit earlier, but it costs __ and arrives at ___. This flight has a minimal layover, but it leaves at ___ and costs ___"). In contrast, the interface Hipmunk has developed makes it exceedingly easy to view all the variables at once, and to quickly narrow down flights I'd potentially be interested in. Not only is the timeline interface much easier to understand than say expedia's "sort results by one variable at a time", but it's an intuitive way to compare the overall utility of multiple flights at once. And since at the end of the day that's exactly what I'm looking for in a travel website - an intuitive way to quickly compare numerous options and choose the 'best' one according to my personal heuristics - I use Hipmunk when I need to book a flight.