Comment 16 for bug 549799

With the introduction of Unity in 11.04, the behaviour of update notification has again changed fundamentally: The notification area icon was entirely dismissed and the Update Manager now shows up in the Unity launcher on new updates (with its window in the background).
I'm not sure about other desktop environments like GNOME 3 or Xfce, but for the "official" Ubuntu desktop this bug no longer seems to be an issue.