I was getting ready to say almost the exact same thing -- thank heavens that Hipmunk came when it did, or that acquisition (if soured) would have left a very large hole in my travel-making tools.

I don't particularly like Kayak, but as a matter of effectiveness, there's no doubt that it was pretty much king of the hill for a good long while. Since Hipmunk's inception though, it has definitely been the 'go-to' place for travel-planning, and beats the nearest competition (that I've used) by a mile.

I would also venture to say that this was perhaps a timely exit for Kayak, as the more and more traction Hipmunk sees, the less off the Kayak founders would have been for an exit.