1. A method for providing a response to a user request, comprising: at a server computer with one or more processors and memory: receiving a user request from a mobile client device, the user request including at least a speech input and seeks an informational answer or performance of a task; detecting a failure to provide a satisfactory response to the user request; in response to detecting the failure, crowd-sourcing information relevant to the user request by querying one or more crowd sourcing information sources; receiving one or more answers from the crowd sourcing information sources; and generating a response to the user request based on at least one of the one or more answers received from the one or more crowd sourcing information sources.