The usual behaviour when clicking twice on an icon in the unity launcher is to trigger the scale mode: all windows of that app are tiled.
Now, a third click triggers different kinds of behaviour: most of the time it does nothing, sometimes it exits scale mode, and sometimes (not easily reproducible) it shuffles windows around, so for instance if I have Evolution open, and I am editing a message, clicking twice will show the message on the right and Evolution on the left, and a third click will shift the message to the left, and Evolution to the right.
I was wondering what would cause these different behaviours, and is it possible to control them (the second option is most useful, it would be nice for this to be consistent).
Bonus question: is there any purpose to shifting windows around as in the third behaviour, except to impress colleagues?
I'm not sure there's an answer to this question. It's an ongoing process to find the best behavior, and you'll find a couple of long discussions about it on the Ayatana mailing list. The way it is in 11.04 is just the way it is, and it definitely has its flaws.