12. A computer-implemented method for facilitating a search, comprising: under control of one or more computer systems configured with executable instructions, categorizing at least some of a first plurality of items included in a search result set of items into at least one of a plurality of categories arranged in a category hierarchy having a root category; selecting a second plurality of items from the first plurality of items based at least in part on one or more search terms and independent of categories in the category hierarchy other than the root category; selecting a plurality of refinements from a set of refinements based at least in part on the one or more search terms and a map depicting a plurality of associations between search terms and categories of the category hierarchy, and links between the categories and the set of refinements; receiving a selection of at least one of the plurality of refinements linked to the at least one of a plurality of categories; maintaining a log of a number of times the at least one refinement of the plurality of refinements is selected during searches employing the one or more search terms in one or more time periods; determining a possibly relevant set of categories of the category hierarchy below a distinguished category based at least in part on the log; increasing an associative confidence between at least one of the one or more search terms and a subset of the set of refinements linked to the possibly relevant set of categories based at least in part on the log; determining the subset of the set of refinements linked to the possibly relevant set of categories when the associative confidence at least meets a first sufficiency threshold; providing said subset of the set of refinements for presentation; and constraining subsequent search result sets to a particular distinguished category, based at least on the one or more search terms, when the associative confidence meets at least a sufficiency second threshold.
12. A computer-implemented method for facilitating a search, comprising: under control of one or more computer systems configured with executable instructions, categorizing at least some of a first plurality of items included in a search result set of items into at least one of a plurality of categories arranged in a category hierarchy having a root category; selecting a second plurality of items from the first plurality of items based at least in part on one or more search terms and independent of categories in the category hierarchy other than the root category; selecting a plurality of refinements from a set of refinements based at least in part on the one or more search terms and a map depicting a plurality of associations between search terms and categories of the category hierarchy, and links between the categories and the set of refinements; receiving a selection of at least one of the plurality of refinements linked to the at least one of a plurality of categories; maintaining a log of a number of times the at least one refinement of the plurality of refinements is selected during searches employing the one or more search terms in one or more time periods; determining a possibly relevant set of categories of the category hierarchy below a distinguished category based at least in part on the log; increasing an associative confidence between at least one of the one or more search terms and a subset of the set of refinements linked to the possibly relevant set of categories based at least in part on the log; determining the subset of the set of refinements linked to the possibly relevant set of categories when the associative confidence at least meets a first sufficiency threshold; providing said subset of the set of refinements for presentation; and constraining subsequent search result sets to a particular distinguished category, based at least on the one or more search terms, when the associative confidence meets at least a sufficiency second threshold. 18. A computer-implemented method according to claim 12 , wherein ordering the plurality of refinements comprises determining a popularity score for at least some of the plurality of refinements.