Modal buttons (i.e. buttons that change their behaviour depending on various environmental conditions) are often considered harmful as they often leave the user unsure as to what will happen when they are pressed.

The application launcher buttons in overview mode appear to be an example of this: when an application isn't running, clicking on its button opens a new window; but if it is running, clicking on its button raises all the existing windows belonging to that application.

For example:
1. Clicking on the "Terminal" launcher icon when gnome-terminal isn't running opens a new terminal window.
2. Clicking on the "Terminal" launcher icon when there are 10 existing gnome-terminal windows open simply raises all 10 windows at once.

This leaves the user unsure what the outcome of clicking the "Terminal" icon will be, since they have to consider whether or not there are other Terminal windows open already.  Arguably, raising 10 existing terminal windows is unlikely to ever be what the user wants - clicking the Terminal launcher should consistently do the same thing each time, open a new gnome-terminal window.  If the user wants to raise a specific window, Overview mode already provides a consistent interface to do this by allowing the user to click on the Exposé-style shrunken windows.

This problem is even more apparent with Empathy: Clicking on the Empathy launcher icon will cause the contacts window to appear, except if any chat windows are already open they are raised instead and there is no obvious way of accessing the contacts window again (the answer is to right-click the Empathy icon and select "New Window", but this is very unintuitive since it is completely different to the method the user would've used to open the contacts window originally.