13. A system comprising: one or more processing devices; and a non-transitory computer-readable medium coupled to the one or more processing devices having instructions stored thereon which, when executed by the one or more processing devices, cause the one or more processing devices to perform operations comprising: storing, in a bookmark database, resource identifiers for a first user; receiving a request by the first user to expose, to a second user, a particular resource identifier that is stored for the first user in the bookmark database; exposing the particular resource identifier to the second user; storing the particular resource identifier for the second user in the bookmark database; receiving a search query from the second user; generating a result set based on searching a global index and resource identifiers that are stored for the second user in the bookmark database, wherein the result set includes the particular resource identifier; and outputting the result set.
13. A system comprising: one or more processing devices; and a non-transitory computer-readable medium coupled to the one or more processing devices having instructions stored thereon which, when executed by the one or more processing devices, cause the one or more processing devices to perform operations comprising: storing, in a bookmark database, resource identifiers for a first user; receiving a request by the first user to expose, to a second user, a particular resource identifier that is stored for the first user in the bookmark database; exposing the particular resource identifier to the second user; storing the particular resource identifier for the second user in the bookmark database; receiving a search query from the second user; generating a result set based on searching a global index and resource identifiers that are stored for the second user in the bookmark database, wherein the result set includes the particular resource identifier; and outputting the result set. 14. The system of claim 13 , wherein exposing the particular resource identifier to the second user comprises providing the resource identifier for display to the second user.