I've been a notorious GNOME Shell apologist ever since it was released (before, for that matter), but there's always been one thorn in my side with the Shell: it completely ruined IRC notifications, for me. Empathy is supposed to have a whizzy notification system, but every time I've tried it I've never had much success with it as an IRC client, so that was out. I use xchat-gnome, because I'm used to it and it does everything I want an IRC client to do, and with GNOME 2.x it would pulse the Xchat window's entry in the task list (ahh, remember task lists) when someone had said something to me. I could always see if there was a PM or adamw: I hadn't read yet. Simple. In Shell, instead I get a little notification that shows up at the bottom corner of the screen for a couple of seconds, if I happen to be paying attention, then disappears, unless I go looking for it in the overview. It's usually less trouble just to alt-tab to the xchat window and look there, which comprehensively kills the 'distraction-free computing' idea.
Anyhow, now I can quit bellyaching about that, because the awesome message notifier extension makes things much better. Now when someone says something to me on IRC I get a much more noticeable notification, one of the 'important' ones that shows up in the middle-bottom of the screen, is a lot bigger than the bottom-right corner notifications, and doesn't go away until I tell it to. Also, it actually tells me what the message was. Glorious! I am a happy IRCer once more. Thank you, Marco, if we ever wind up at some event or other, consider me to owe you many drinks.