1. A computer-implemented method, comprising: recording item selection events in which users select particular items represented in an electronic data repository, said items arranged in a hierarchical browse structure that comprises multiple levels of item categories; generating relative preference profiles for particular users, each relative preference profile representing preferences of a respective user for particular item categories of said hierarchical browse structure relative to corresponding preference levels of a population of users, wherein generating the relative preference profiles comprises analyzing the recorded item selection events to assess users' preferences for particular item categories, wherein the relative preference profile for a user comprises a plurality of relative preference scores, each relative preference score corresponding to a respective item category and reflecting a degree to which the user's preference level for the item category differs from the user population's preference level for the item category; and selecting items to recommend to users based at least partly on the relative preference profiles of the users; said method performed in its entirely by a computer system.