I've just switched on my laptop. The notifier told me there are a couple of updates available, and I click on the icon on the gnome tray. The usual gksudo dialog appears, and then I click I want to update my system. Then I switch the focus back to Firefox, to continue browsing. Just a moment later, update-manager takes back the focus to show me the packages it's going to install. Again, I click "do it", and switch back to firefox. The update manager then takes back the focus to show me the "I'm downloading packages" dialog, and I switch back the focus to firefox, just to find that a moment later, the app once more grabs the focus to show me it's installing the packages, and once more, a bit later, to tell me it's finished (then it takes me to the initial window).
This is really annoying. I understand it should ask me for confirmation when it's going to install the packages, but not grab the focus (maybe the app bar could "blink" like other apps do), and once I do that, not grab the focus anymore on its own. When I finish what I'm doing, I'll close the update manager on my own, if it has finished updating.
Thanks for the great work!
Note that the update-notifier is also rather invasive; see bug #73718 for more details.