18. An apparatus comprising a processor coupled to a memory, the memory holding instructions for: receiving user-defined lists of content identifiers for corresponding user accounts at a client device, wherein the user-defined lists of content identifiers define collections of recorded audio and video works for respective ones of the user accounts; receiving user input identifying permitted social group members for an authorized user, and transmitting identifiers for the permitted social group members to a server for developing social group information for the authorized user; arranging a matrix of images representing contents of one of the user-defined lists of content identifiers for the authorized user, so that each image in the matrix corresponds to a different one of the content identifiers and size of each image in the matrix depends on a popularity score for each content identifier, being a measure of relative frequency with which a corresponding one of the content identifiers appears in the user-defined content lists; arranging the matrix of images depending on each popularity score, wherein the popularity score is at least one of: (a) a measure of relative frequency with which a corresponding one of the content identifiers appears in the user-defined content lists for permitted social group members of the authorized user only, or (b) a measure of relative frequency with which a corresponding one of the content identifiers appears in the user-defined content lists for other users in addition to permitted social group members of the authorized user; and outputting information for display of a user interface on the client device, the interface comprising the matrix of images.
18. An apparatus comprising a processor coupled to a memory, the memory holding instructions for: receiving user-defined lists of content identifiers for corresponding user accounts at a client device, wherein the user-defined lists of content identifiers define collections of recorded audio and video works for respective ones of the user accounts; receiving user input identifying permitted social group members for an authorized user, and transmitting identifiers for the permitted social group members to a server for developing social group information for the authorized user; arranging a matrix of images representing contents of one of the user-defined lists of content identifiers for the authorized user, so that each image in the matrix corresponds to a different one of the content identifiers and size of each image in the matrix depends on a popularity score for each content identifier, being a measure of relative frequency with which a corresponding one of the content identifiers appears in the user-defined content lists; arranging the matrix of images depending on each popularity score, wherein the popularity score is at least one of: (a) a measure of relative frequency with which a corresponding one of the content identifiers appears in the user-defined content lists for permitted social group members of the authorized user only, or (b) a measure of relative frequency with which a corresponding one of the content identifiers appears in the user-defined content lists for other users in addition to permitted social group members of the authorized user; and outputting information for display of a user interface on the client device, the interface comprising the matrix of images. 22. The apparatus of claim 18 , wherein the memory further holds instructions for augmenting the one of the user-defined lists of content identifiers for the authorized user, in response to user input indicating addition or removal of a recorded audio or video work.