I've been thinking about compact progress indicators for a while already, and circular indicator seems to be the most clear and obvious, but it's horrible from design point of view, because circle is the least compact shape of all and you'll have to make it too small if you want it to look OK. Gnome-system-monitor already has those, you can see what they look like in there. We need a more eyecandy and still clear and abstract shape for that, I have no idea what can it be.<br>
By the way, it's better to discuss this in Ayatana mailing list. It's their job to mess with stuff like that.<br>