15. The system of claim 13 , wherein storing, in the bookmark database, resource identifiers identified for the first user comprises storing, in the bookmark database, a first set of resource identifiers for the first user, wherein the first set of resource identifiers includes the particular resource identifier.
15. The system of claim 13 , wherein storing, in the bookmark database, resource identifiers identified for the first user comprises storing, in the bookmark database, a first set of resource identifiers for the first user, wherein the first set of resource identifiers includes the particular resource identifier. 16. The system of claim 15 , wherein storing the particular resource identifier for the second user comprises updating a second set of resource identifiers for the second user to include the particular resource identifier, wherein the second set of resource identifiers is stored in the bookmark database.