20. The non-transitory computer storage of claim 13 , in combination with a computer system that executes said instructions to perform said method.
13. Non-transitory computer storage having instructions stored thereon which cause a computer system to perform a method of selecting items to recommend to a target user, the method comprising: outputting a user interface that provides functionality for users of an electronic catalog of items to create and assign arbitrary textual tags to individual items represented in the electronic catalog after selecting said items, such that the textual tags categorize the items represented in the electronic catalog, the user interface comprising a tag entry field on item detail pages of the electronic catalog, the tag entry field enabling the users to create the tags via entry of text strings into the tag entry field; programmatically identifying at least one tagged item in the electronic catalog, the at least one tagged item selected by a target user, without receiving a designation from the target user of the at least one tagged item; subsequent to and in response to said identifying, selecting one or more user-defined textual tags associated with the at least one tagged item by at least identifying a threshold number of most popular tags assigned to the at least one tagged item, without any input from the target user, each tag comprising a descriptor selectively associated with the at least one tagged item by one or more users; automatically searching the electronic catalog using the one or more tags as keywords to identify a corresponding set of related items; selecting at least a portion of the set of related items to provide as recommendations to the target user; and outputting the recommendations with associated textual reasons for recommending the items.