Selecting advertisements to deliver to a user of an electronic application system. Selecting includes storing a plurality of user defined object types for defining attributes of user contributed objects, and storing a plurality of user contributed objects, each having an object type. Selecting further includes receiving from a user a request for one or more of the stored objects, wherein at least one of the requested objects has a user defined object type, and selecting an advertisement to provide to the user based at least in part on the user defined object type of the one or more requested objects.