9. A system comprising: one or more computers; and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: selecting one or more users that are connected to a particular user by way of a social networking service or by a relationship described by a graph stored in a database, wherein each user interacts with one or more services; obtaining, for each of the selected users, interest data indicating past interactions of the selected user that are associated with a particular topic and that are of different interaction types; selecting a model that is used for generating the interest score of the particular user that reflects the particular user's predicted interest in the particular topic from a set of two or more models each corresponding to a different topic, wherein the interest score of the particular user is generated based at least on the interaction types of the past interactions indicated by the interest data of the selected users as being associated with the particular topic; applying the interest data of the selected users for the particular topic to the model to generate the interest score of the particular user for the particular topic; receiving a search query associated with the particular topic from the particular user; determining, for each search result that is responsive to the search query, a search query score that reflects a likelihood that the search result corresponds to the search query; ranking the search results based on the interest score of the particular user for the particular topic and the search query scores; and providing a search results page based on the ranking of the search results.
9. A system comprising: one or more computers; and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: selecting one or more users that are connected to a particular user by way of a social networking service or by a relationship described by a graph stored in a database, wherein each user interacts with one or more services; obtaining, for each of the selected users, interest data indicating past interactions of the selected user that are associated with a particular topic and that are of different interaction types; selecting a model that is used for generating the interest score of the particular user that reflects the particular user's predicted interest in the particular topic from a set of two or more models each corresponding to a different topic, wherein the interest score of the particular user is generated based at least on the interaction types of the past interactions indicated by the interest data of the selected users as being associated with the particular topic; applying the interest data of the selected users for the particular topic to the model to generate the interest score of the particular user for the particular topic; receiving a search query associated with the particular topic from the particular user; determining, for each search result that is responsive to the search query, a search query score that reflects a likelihood that the search result corresponds to the search query; ranking the search results based on the interest score of the particular user for the particular topic and the search query scores; and providing a search results page based on the ranking of the search results. 10. The system of claim 9 , wherein the model indicates different weights corresponding to different types of interactions.