If you think Yahoo has given up on search, think again. The company may have handed its back-end search operations to Microsoft, but Marissa Mayer thinks there's work to be done on mobile devices, particularly around contextual search. Contextual search aims to give people the right information, at the right time, by looking at signals such as where they're located and what they're doing -- such as walking or driving a car. Mobile devices tend to provide a lot more of those signals.