7. A method of enabling a user to obtain focused item recommendations for a user-specified category of items, the method comprising: by one or more computer systems comprising computer hardware: providing a tagging interface that provides functionality for a user to create tags for classifying items represented in an interactive catalog via entry of text strings into tag fields of item detail pages of the catalog, the item detail pages each comprising information descriptive of a catalog item in an interactive catalog of items; persistently storing tag data of the user in a data repository, the tag data specifying tags and tag-item associations created by the user via the tagging interface; outputting for display to the user one or more of the tags created by the user; and generating tag-specific item recommendations, said generating comprising: receiving a user selection of a displayed tag of the one or more tags output for display to the user; programmatically accessing the tag data in response to receiving the user selection of the displayed tag, to thereby identify at least one of the catalog items previously tagged with the displayed tag by the user, without requiring further user interaction, programmatically accessing item relationship data to identify a set of additional items that are related to the catalog items previously tagged by the user with the displayed tag, and selecting at least a portion of the additional items to recommend to the user as the tag-specific item recommendations.
7. A method of enabling a user to obtain focused item recommendations for a user-specified category of items, the method comprising: by one or more computer systems comprising computer hardware: providing a tagging interface that provides functionality for a user to create tags for classifying items represented in an interactive catalog via entry of text strings into tag fields of item detail pages of the catalog, the item detail pages each comprising information descriptive of a catalog item in an interactive catalog of items; persistently storing tag data of the user in a data repository, the tag data specifying tags and tag-item associations created by the user via the tagging interface; outputting for display to the user one or more of the tags created by the user; and generating tag-specific item recommendations, said generating comprising: receiving a user selection of a displayed tag of the one or more tags output for display to the user; programmatically accessing the tag data in response to receiving the user selection of the displayed tag, to thereby identify at least one of the catalog items previously tagged with the displayed tag by the user, without requiring further user interaction, programmatically accessing item relationship data to identify a set of additional items that are related to the catalog items previously tagged by the user with the displayed tag, and selecting at least a portion of the additional items to recommend to the user as the tag-specific item recommendations. 8. The method of claim 7 , wherein identifying the set of additional items comprises identifying the additional items from item relationship data, the item relationship data comprising item-to-item similarity mappings.