Windows 7 Taskbar Notifications
With Windows XP and Vista, when an application wanted to attract your attention, it would flash its window in the task bar. When it stopped flashing, it would stay a fairly obvious orange colour.
Windows 7 uses a different mechanism, and one I find far too subtle.
Looking at this, you're probably thinking "hey it's obvious, the orange one wants your attention". And it does seem that way, but for some reason I find myself, with Windows 7, missing IM notifications and not responding to messages until hours later, because I just didn't notice that I had a new message.
Maybe it's because of all the additional noise in the taskbar - it's harder to tell at a glance that an app wants your attention, so I don't pick it up "out of the corner of my eye" the way I would with the XP style.
The Mac continues to animate icons that want your attention until you give in and click on it. Windows animates the icon for a few seconds and then settles on the orange look. One solution would be to change Windows 7 so that the animation continues until you respond.