1. A method of personalizing a search of a document collection to a user, the method comprising: monitoring a plurality of documents accessed by the user; identifying a plurality of first phrases present in one or more of the accessed documents; receiving a query from the user, the query including one or more second phrases; selecting a plurality of documents selected from the document collection that are responsive to the query; identifying one or more of the first phrases as related phrases that are related to the one or more second phrases, wherein a particular related phrase is related to a particular second phrase when an information gain exceeds a threshold, the information gain being a ratio of an actual co-occurrence rate of the particular related phrase and the particular second phrase in documents of the document collection and an expected occurrence rate of the particular related phrase and the particular second phrase in the documents; weighting a plurality of scores, each score corresponding to a respective document of the plurality of selected documents responsive to the query, wherein the score of the respective document that includes the one or more related phrases is boosted by the weighting; ranking the plurality of selected documents for presentation to the user based on their corresponding weighted scores, to provide personalized search results; and presenting the personalized search results to the user.