Yeah, that's a rather important feature, given that airlines often run certain flights only on certain days. I don't personally do much business travel, so when I fly, my dates are extremely flexible.

It also seems to completely lack EasyJet, which makes it nearly useless for intra-Europe flights.

I've seen quite a lot of Hipmunk hype, and it does have a nice UI that presents information well. But in terms of actually finding the cheapest flight in a given time window, I'll stick with Kayak.