Only if it hasn't a "Volume Up" symbol on it and/or if the standard functions have been enabled via System Preferences > Keyboard, unless the OP has a very old Mac.
New MBP. F11 has vol down symbol. Looks like I'd need to disable all the special symbol functions in the keyboard prefs in order to assign one to Expose's show desktop function. Not worth loosing all the other special functions. Be better if I could just re-assign the F4 dashboard key to show desktop instead since I don't use dashboard.
Actually, I don't like the way expose does the show desktop by sliding everything up and making that border around the screen as a temp situation. I'd rather it just be exactly like the normal desktop with all other windows and apps hidden. It seems there used to be a command for that in the old Mac OS.
This is the closest to what I'm wanting, but it doesn't hide Finder windows, so it isn't exactly what I want. But I still greatly prefer it to the Expose method of showing the desktop.
I've assigned the Finder to Desktop 1 and get to it using Control 1, just like I did in Snow Leopard. Having Finder windows open isn't a problem for me and takes a millisecond to close them if I want to.