1. A method of analyzing search behavior, the method comprising: storing, by one or more computers, data associated with searches and user behavior with regard to a plurality of search results produced by the searches; identifying, by the one or more computers, a session comprising one or more related search results in the plurality of search results; prior to calculating one or more relevance factors: processing, by the one or more computers, the data to determine search queries that were used to locate each search result in the session; processing, by the one or more computers, the data to determine click-through behavior for each search result in the session; and processing, by the one or more computers, the data to obtain explicit feedback on search results in the session; calculating, by the one or more computers, the one or more relevance factors for each search result in the session, wherein a relevance factor for a search result is data that describes an aspect of user behavior regarding the search result, and wherein calculating the one or more relevance factors comprises: calculating, by the one or more computers, the one or more relevance factors using the search queries that were used to locate each search result in the session; calculating, by the one or more computers, the one or more relevance factors using the click-through behavior for each search result in the session; and calculating, by the one or more computers, the one or more relevance factors using the explicit feedback on each search results in the plurality of search results; determining a first user behavior profile based on one or more relevance factors for search results in the plurality of search results having explicit feedback indicating that the search results are acceptable; determining a second user behavior profile based on one or more relevance factors for search results in the plurality of search results having explicit feedback indicating that the search results are not acceptable; and assigning a relevance classification of acceptable to a given search result in the session when the relevance factors for the given search result are similar to the relevance factors for the first user behavior profile, wherein no explicit feedback is provided for the given search result; assigning, by the one or more computers, a relevance classification of unacceptable to the given search result when the relevance factors for the given search result are similar to the relevance factors for the second user behavior profile.