A little tip I found a while back that I very much enjoy: the default Mac OS X Leopard dock looks like glass and reflects the desktop and application icons. I wanted to turn that off (have it reflect nothing), and it turns out that this is how one does that:
In Terminal, to turn the glass dock off, type
defaults write com.apple.dock no-glass -boolean YES; killall Dock
and to turn it back on, type
defaults write com.apple.dock no-glass -boolean NO; killall Dock
You’re welcome!