A nice article on the MSDN Blogs The Old New Thing entitled I bet somebody got a really nice bonus for that feature. It goes through what the quicklink menu, taskbar, and balloon help should be used for, as opposed to being cluttered up with useless crap by pretty much every app you install these days. A good / must read for application developers on the windows platform.

The rule for taskbar notifications is that they are there to, well, notify the user of something. Your print job is done. Your new hardware device is ready to use. A wireless network has come into range. You do not use a notification icon to say "Everything is just like it was a moment ago; nothing has changed." If nothing has changed, then say nothing.