23. The computer system of claim 19 , wherein the instructions for determining the popularity metric of a candidate search result further include: instructions for determining a model predicting a likelihood of a user selection of a search result using multiple users' search histories; and instructions for applying the model to the user's search history to generate the popularity metric of the candidate search result.
23. The computer system of claim 19 , wherein the instructions for determining the popularity metric of a candidate search result further include: instructions for determining a model predicting a likelihood of a user selection of a search result using multiple users' search histories; and instructions for applying the model to the user's search history to generate the popularity metric of the candidate search result. 24. The computer system of claim 23 , wherein the instructions for determining the model further include: instructions for generating a profile that characterizes the multiple users' behaviors over multiple search results in the multiple users' search histories; and instructions for determining as the model a set of coefficients from the profile, wherein the set of coefficients, when applied to a set of search results associated from a specific user's search history, is configured to predict the likelihood of the specific user's selection of each of the search results in the future.