-d significa release de desenvolvimento, e isso seria Oneiric. Basta executá-lo sem a bandeira e você receberá atualizações regulares.
egil@morgenstern [~] $ update-manager --help
Usage: update-manager [options]
Options:
-h, --help show this help message and exit
-V, --version Show version and exit
--data-dir=DATA_DIR Directory that contains the data files
-c, --check-dist-upgrades
Check if a new Ubuntu release is available
-d, --devel-release Check if upgrading to the latest devel release is
possible
-p, --proposed Upgrade using the latest proposed version of the
release upgrader
--no-focus-on-map Do not focus on map when starting
--dist-upgrade Try to run a dist-upgrade
--no-update Do not check for updates when starting
-s, --sandbox Test upgrade with a sandbox aufs overlay