- Tagger todos:
  - add missing tests
  - finish similar objects method
  - duplicate insert detection in tag()
  - add routes and controllers for objects and users
  - some sort of db_select object for more reliable sql generation

- implement split read/write database support through Horde_Db, also allowing
  for sharding, multi-master, backup connections, etc. Probably will take a
  Horde_Db_ConnectionManager object or some such, that can implement logic for
  which connection to use.

- interface for doing tag searches via technorati, google, etc. (take a tag in
  the system, find things with the same tag on other systems).

- linkbacks addition: instead of just tracking linkbacks we're directly notified
  of, also provide a way to search for links to the resource in question (google
  link: search, etc).