Look at this picture (running without Aero, which still isn't supported on VMWare Fusion). One of the key tasks in a toolbar is to be able to determine which applications are running just by looking. It is possible to do so with the above visual representation, but it is really hard.
If you look carefully, you will notice that the 1st, 3rd, and 5th applications are currently active (Firefox, Word, and Snip). But it is so hard to tell because the visual representation of running applications is a simple rectangle around the edge of the icon. In this situation, this just doesn't work for a few reasons:
- The top and bottom edges of the rectangle are lost because they run up against the edges of the toolbar
- The left and right edges of the rectangle are exactly midway between the icon they intend to indicate, and the neighboring icon. Thus, you can't tell which icon is being highlighted.
- In general, rectangular outlines are a poor way to highlight objects because when a person's eye is focused on an icon, it is a "global" cognitive task to integrate lines around the edge and determine that they surround an object. Alternatively, a much simpler "local" cognitive task is to determine the background color, or if a simple visual indicator is present. (Umm, see a competing operating system to see how well a little glowing triangle under the active application works for this task).
But this is pretty straightforward stuff, and it should really be perfect.