1. A computer-implemented method of facilitating user management of a collection of items, the method comprising: maintaining an item collection of a user in computer storage; applying a clustering algorithm to the item collection to subdivide the collection into multiple clusters of items, said clusters generated based, at least in part, on calculated distances between the items; displaying the multiple clusters to the user via an interface that enables the user to associate metadata with specific clusters of items, and receiving cluster-level metadata from the user, said cluster-level metadata corresponding to a cluster selected by the user, said cluster comprising a plurality of items; using the cluster-level metadata, in combination with data regarding the collection of items, to generate personalized item recommendations for the user; and outputting a representation of the personalized item recommendations for presentation to the user.