From Social Patterns
People sometimes want information or advice that can't be found in a neutral, objective reference guide and would ask another human being directly if they could find someone interested in or knowledgeable about the topic of their question.
Use this pattern when you wish to foster communication and cooperation among the people using your social application.
Provide a large inviting text-entry box to encourage questioners to write full sentences (like a human being) instead of query strings or boolean operators, and label the form button with a word like "Ask"
At the same time, expose open questions to people as a way of inviting them to answer (or route questions to likely, willing answerers based on affinities you derive from the metadata in your social graph).
Alternately, as Aardvark does, rely on existing conversational channels (primarily in the case of Aardvark, IM) for capturing questions, routing to potential respondees, and delivering answers.
Optionally, embrace a reputation system to help ferret out the best contributors and the most helpful answers.
Directly querying an index of data is a great way of searching for information, with historical roots going back to the earliest libraries, archives, and repositories, but people have always gathered information in other ways as well. In fact, most people in the real world ask other human beings for information as a starting point.