18. The physical computer storage of claim 16 , wherein the executable code directs the computing system to compare item attributes of the first and second items to determine whether said threshold degree of similarity is met.
16. Physical computer storage that stores executable code that directs a computing system to at least: receive a recommendation set generated by a recommendation engine, said recommendation set comprising a computer representation of a plurality of items predicted to be of interest to a target user; filter the recommendation set to increase a degree of item diversity of the recommendation set, said filtering comprising filtering out a first item from the recommendation set based at least partly on a determination that the first item has at least a threshold degree of similarity to a second item in the recommendation set, said first and second items not being duplicates of each other; and output at least a portion of the filtered recommendation set for presentation to the target user with a display element that enables the target user to initiate a display of one or more items, including said first item, that were filtered from the recommendation set.