1. A computer-implemented method, comprising: maintaining user-defined lists of content identifiers in a computer memory for corresponding user accounts, in response to user input defining collections of recorded audio and video works for respective ones of the user accounts; maintaining social group information for each of the user accounts, in response to user input identifying permitted social group members for respective ones of the user accounts; providing, from a server to a client device for a first user, information about user-defined content lists maintained for permitted social group members of the first user; determining popularity scores each of which pertains to a different content identifier based on frequencies with which the ones of the content identifiers appear in the user-defined content lists; selecting the user-defined content lists for determining the popularity scores for the first user from at least one of: (a) lists consisting of the user-defined content lists for permitted social group members of the first user, or (b) lists including user-defined content lists for users that are not in the permitted social group for the first user; and providing image data and associated ones of the popularity scores to the client device to enable display of distinct images each corresponding to a different content identifier in a matrix of images, the matrix representing contents of corresponding ones of the user-defined lists on the client device wherein display size of each image in the matrix is determined at least in part by an associated one of the popularity scores determined for each content identifier.