[smartera]

Other than flexible dates and more search options, Kayak has direct search links to the airlines. Google flights (while having brilliant map search) asks you to call a travel agency and in many cases the price was not as accurate as Kayak

[Dwolb]

This is surprising to me because Kayak uses ITA Software [1] which is owned by Google. Perhaps Kayak has better relationships with the airlines than Google and cultivates more accurate pricing this way.

[1] http://www.itasoftware.com/index.html