I have Unsanity's WindowShade X app set to make a window transparent when you double-click on the title bar. I've found that if you click with the right and left mouse buttons at the same time, Window Shade X sees that as a double-click, and makes the window transparent. Not much of a time saver, but just interesting.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060817210659510