1. A computer-implemented method of searching for and presenting content items as an arrangement of conceptual clusters to facilitate further search and navigation on a display-constrained device, the method comprising: providing a relatively large set of content items, at least some of the content items having metadata to specify explicit concepts associated with the content items, and at least some of the metadata including phrases having more than one metadata term; receiving from a user incremental input to incrementally identify more than one search term for desired content items; selecting from the relatively large set of content items: a first set of content items, wherein all search terms match metadata terms of a single one of the metadata phrases of each content item of said first set; a second set of content items, wherein a first subset of the search terms matches at least one metadata term of at least a first metadata phrase of each content item of said second set; and a third set of content items, wherein a second subset of the search terms matches at least one metadata term of at least a second metadata phrase of each content item of said third set, the first metadata phrase differing from the second metadata phrase; grouping the content items the second and third sets have in common to form an intersection set for user-implied concepts inferred from the explicit concepts associated with the metadata of the content items of the intersection set; organizing the content items of the first set and the intersection set into conceptual cluster sets: the content items of the first set being organized into explicit conceptual cluster sets based on the metadata phrases having metadata terms matching the search terms so that content items having a same metadata phrase matching the search terms are clustered together; and the content items of the intersection set being organized into user-implied conceptual clusters based on at least the first and second metadata phrases the content items of the intersection set have in common so that content items having same first and second metadata phrases matching the search terms are clustered together; and presenting on the display-constrained device the content items organized into the explicit conceptual cluster sets and the user-implied conceptual cluster sets: each explicit conceptual cluster set identified based on the metadata phrase common to the content items of said explicit conceptual cluster set having metadata terms matching the search terms; and each user-implied conceptual cluster set identified based on the first and second metadata phases the content items of said user-implied conceptual cluster set have in common.