1. A method comprising: in an electronic data repository, storing individually addressable document elements for a plurality of documents, each of at least some of the document elements having one or more associated topics; and using one or more computer processors, tracking user interactions with the document elements and storing, for each of the interactions, at least an identifier of the document element interacted with and an identifier of the interacting user; and determining, for each of at least some of the interacting users, at least one of an interest or a field of expertise based at least in part on the tracked user interactions of that user and the topics associated with the interacted-with document elements.