As a college freshmen in 2003, I used my once in a lifetime Apple Student Developer 20% discount on a stacked PowerMac G5 dual 2.0GHz. I loved that machine and couldn't believe how snappy OS X was on it. The way I tested UI speed then was clicking on a menu item (say the File menu), and moving my mouse back and forth on the other menu items as fast as I could — the G5 was the first computer I had that could keep up and show all of the sub menus in a flash without stuttering.