I'm really not sure what component is supposed to implement update notification, so I'm not sure what to file this against. It may be a dupe, I know mclasen is aware of the problem, but not sure if it's filed in Bugzilla yet. Please close if it's a dupe. In current F15, if using Shell rather than the fallback interface, update notification seems to be broken: you just never get notified of available updates. This is a Beta blocker per criterion "The desktop default update manager must not periodically check for updates when the system is booted live, but must periodically check for updates when running on an installed system".
Matthias seemed to be aware of the problem and think there was a fix somewhere pending from a conversation earlier today, but anyways is not a shell bug.
Discussed at 2011-03-18 blocker review meeting. Accepted as a Beta blocker per criterion cited above.
So, this was fixed in 2.91.91-3: - Add a patch from upstream to fix the updates plugin. I can confirm the fix, I'm seeing update notifications now. 2.91.92-1 is the current 'stable' package, so we can close this report.