For us old-school Mac users, AppleInsider's Road to Mac OS X Leopard: System Preferences article really brings back memories. It walks through the evolution of Mac System Preferences (formerly known as Control Panels) going all the way back to 1984 and ending up at Mac OS X Leopard, which was released last week.
Simply scrolling through the article provides an interesting view of the process of revision in software design. The original Control Panel (which was technically a Desk Accessory named "Control Panel") was brilliantly simple, if a little cramped -- it controls roughly nine different functions all in a 315x177 pixel window. Clever use of icons (rather than text labels) enables the panel to be very efficient in its use of screen real estate, and also means it doesn't need to be translated for non-English operating system releases.
Watching the Control Panel expand to meet the growing needs of the Mac system, you can watch the system designers trying out various strategies for cramming in more information in a similar space. At one point (ahem, System 7) the unified "Control Panel" interface is abandoned in favor of a folder full of mini-applications -- more clicks to open and close them, but lots more flexibility in design for each one. This approach becomes untenable in Mac OS 8 and 9 as the sheer number of Control Panels makes it very hard to find what you're looking for, just by browsing in a Finder window.
As Mac OS X enters the picture, the designers finally hit on a method that works for them -- a scrolling menu of panels on the top, with the panel below. Ironically, this is very similar to the menu-on-the-left design of the Control Panel in 1987. In later Mac OS X releases, this approach is refined, with lots of attention focused on grouping and organizing the panels so related things are near each other.
Anyway, if you're into Mac geek history, check it out. (You may also appreciate this earlier post about Mac history.) And just try to tell me those 80's black and white Control panels don't bring you straight back to the beige 80's!