Kayak is great (was?) but Hipmunk is more than up to the task of filling the void if Priceline ruin Kayak. Congrats to the Kayak folks I guess, when they got into the industry they really raised the bar. Before Kayak I remember having to use Expedia and Orbitz and just having to accept their crappy UI because there simply were no alternatives.
http://www.google.com/flights/?hl=en&gl=us#search;f=LAX;... versus http://www.hipmunk.com/flights/LAX-to-SFO#!dates=Nov09,Nov16... I respect what Hipmunk is trying to do, but I really doubt they are filling voids outside of "this" community. I find it much harder to scan, slower to load, and having lower quality tools for finding alternate (or cheaper) fares.
http://www.tripadvisor.com/CheapFlights?geo=1&travelers=...
More Kayak-like in terms of the results list. Cheapest rates match Hipmunk, though curiously for different flights.