16. A non-transitory, computer-readable media comprising instructions operable, when executed by one or more computing systems, to: receive a request from a first user for a content page; determine a page identifier for the requested content page; determine, based on the page identifier, one or more second users, wherein the one or more second users are identified in the requested content page; determine a plurality of content items based on one or more of the second users, wherein each of the plurality content items is owned by a second user; determine user features of the first user; determine for each of the content items one or more content features; calculate for each of the content items an expected value of the content item with respect to the first user based on the user features of the first user and the content features of the item; order the content items by decreasing expected value; and deliver to the first user, with the requested content page, one or more of the content items as recommendations to the first user based on the ordering of the content items.
16. A non-transitory, computer-readable media comprising instructions operable, when executed by one or more computing systems, to: receive a request from a first user for a content page; determine a page identifier for the requested content page; determine, based on the page identifier, one or more second users, wherein the one or more second users are identified in the requested content page; determine a plurality of content items based on one or more of the second users, wherein each of the plurality content items is owned by a second user; determine user features of the first user; determine for each of the content items one or more content features; calculate for each of the content items an expected value of the content item with respect to the first user based on the user features of the first user and the content features of the item; order the content items by decreasing expected value; and deliver to the first user, with the requested content page, one or more of the content items as recommendations to the first user based on the ordering of the content items. 18. The media of claim 16 , the instructions further operable, when executed by one or more computing systems, to: calculate for each of the content items the expected values using a respective recommendation model, wherein the recommendation model comprises a set of weights calculated for the first user using one or more statistical models based on the user features of the first user and the content features of the content item; generate an example data point, wherein the data point comprises one of a positive example or a negative example for the user features of the first user and the content features of the content item; and update the set of weights of the respective recommendation model based on the example data point.