Since catching this thread I started playing around with Expose within Safari exclusively. It seems that from a freshly launched Safari, when you open 5 or 6 windows, they will line up in a horizontal row. Once you cross a threshold (I think it's 6 windows) the open windows will instead spread themselves around the screen (not lined up). This makes sense, because you start not being able to tell what's going with ever-shrinking windows. It's nice for the software to fit the windows in as big as they will go, but the action is different each time.
It gets funny when you start playing with what windows you activate. Right now I have three windows open, and every time I activate expose, they go to different places on the screen. This doesn't exactly make me feel good about using it for a highly repetitive task such as tab switching.
It's a cool feature for many windows between apps, but seems limited to that for now.