16. An information retrieval system comprising: at least one processor; a query engine implemented on the at least one processor that receives a query and retrieves a ranked list of items from an index of items; an index generator that generates the index of items at least on the basis of predicted responses of a plurality of target users to a plurality of the items, each of the predicted responses having been generated by: accessing a computer-implemented contacts service to identify a plurality of second users being associated with at least one target user of the plurality of target users by the contacts service; eliciting predicted responses of the at least one target user from the plurality of second users, a predicted response directed toward an item of the plurality of items and indicating an opinion of the item predicted to be held by the at least one target user; storing a second user weight for each of the plurality of second users; calculating a prediction of the at least one target user's response to the item by combining the predicted responses from the plurality of second users using second user weights of the plurality of second users to generate a weighted average of the predicted responses; and a prediction generator arranged to identify at least one item of the plurality of items and the at least one target user of the plurality of target users having a number of predicted responses below a threshold value and elicit, from at least one of the plurality of second users, a predicted response of the at least one target user of the plurality of target users to the at least one item of the plurality of items; wherein, in response to receiving an actual response from the at least one target user indicating an opinion of the item held by the at least one target user, the prediction of the at least one target user's response is provided to the at least one target user.
17. The information retrieval system as claimed in claim 16 wherein the query engine retrieves annotations comprising the predicted responses associated with the ranked list of items.