This is almost not a hint, just one of the smartest keyboard shortcuts I've come up with. Since I don't keep System Preferences in my Dock, I assigned Command-Option-; to launch it from the keyboard. To create the shortcut, open the Keyboard & Mouse System Preferences panel, click on the Keyboard Shortcuts tab, then click the plus sign. In the dialog that appears, leave Applications set to All Applications, set the Menu Title to Preferences..., and enter your desired shortcut in the Keyboard Shortcut box. I used Command-Option-; because it is quite close to the near-universal Command-, shortcut for opening individual application preferences. (Nice touch: in Leopard, the shortcut works immediately!)
[robg adds: This is a very basic hint, but it's a good reminder that the Apple Menu items can all be assigned keyboard shortcuts. For instance, if you move your dock around somewhat regularly, you can assign keyboard shortcuts for the Position on Left/Right/Bottom menu items. (I usually leave my dock at the bottom of the screen, but move it to the right side of my second monitor when using a full-screen app such as Final Cut Express.) Or assign a shortcut to Software Update, to make it easy to repeatedly check for new updates on a day when you're expecting one. Finally, it seems that (as of 10.5, at least), you can also assign keyboard shortcuts for locations in the Location menu. This older hint provided a workaround for older OS X releases, but when I tested a location this morning in 10.5, I was able to activate it via the keyboard shortcut I had assigned to it.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20080605064205753