I really wanted the ability to run custom commands using keyboard shortcuts from my Mac. I don't know why this isn't supported from System Preferences. After a little research I found Butler, a free application launcher for Mac OS X. It does a little more than what I needed, but at least it can be configured to do less.
With very little AppleScript applied it makes a great workspace launcher:
(* Simple App/Workspace Launcher *)
tell application "Terminal" to activate
tell application "Firefox" to activate
tell application "DigitalColor Meter" to activate
tell application "Adium" to activate