13. Non-transitory computer storage comprising instructions stored thereon that, when executed in one or more processors, are configured to implement a system for recommending items to users, the system comprising: a tagging system that provides functionality for a user to: create tags via entry of text strings into tag entry fields of item pages of an electronic data repository, and associate the tags with selected items of the electronic data repository, wherein the tagging system is configured to store user-specific tag data, the user-specific tag data reflecting associations created by the user between the tags and the selected items; the tagging system further configured to output for presentation to the user one or more of the tags created by the user; and a recommendation system configured, to: receive a user selection of a selected tag of the one or more tags output for presentation to the user, and in response to receiving the user selection and without requiring user interaction: identify at least one of the selected items previously tagged with the selected tag, programmatically access item relationship data to identify additional items that are related to the at least one selected item previously tagged by the user, and select one or more of the additional items as recommendations for the user.
13. Non-transitory computer storage comprising instructions stored thereon that, when executed in one or more processors, are configured to implement a system for recommending items to users, the system comprising: a tagging system that provides functionality for a user to: create tags via entry of text strings into tag entry fields of item pages of an electronic data repository, and associate the tags with selected items of the electronic data repository, wherein the tagging system is configured to store user-specific tag data, the user-specific tag data reflecting associations created by the user between the tags and the selected items; the tagging system further configured to output for presentation to the user one or more of the tags created by the user; and a recommendation system configured, to: receive a user selection of a selected tag of the one or more tags output for presentation to the user, and in response to receiving the user selection and without requiring user interaction: identify at least one of the selected items previously tagged with the selected tag, programmatically access item relationship data to identify additional items that are related to the at least one selected item previously tagged by the user, and select one or more of the additional items as recommendations for the user. 17. The non-transitory computer storage of claim 13 , wherein the recommendation system is further configured to generate the recommendations based at least in part on a second tag created by a second user.