Hipmunk needs to ramp up on usability 15 years ago
What most of these commenters seem to completely miss is that if a site is not obvious to a user in 2-6 seconds, it will not work and you will lose users. You cannot expect people to hover here and there nor read FAQs to understand the concepts.
I have nothing against HipMunk, but it does lack a clear value proposition when you land there.