Does OSX Mavericks Have an Equivalent to the F11 Show/Hide Shortcut in Snow Leopard?
First, the keyboard shortcut in 10.6 Snow Leopard (and almost all versions of OS X) for Expose "Show Desktop" is not F11 unless you have 'Use all F1, F2, etc. keys as standard function keys' clicked in System Preferences > Keyboard.

It's actually, by default fn-F11. Exactly the same as it is in 10.9 Mavericks. I suspect that under 10.6 you had the System reversing the standard by clicking the above and got used to that and 10.9 is set to the default where F11 adjusts the volume. Try fn-F11 and it should work. Of course if you want it the other way round then change it in System Preferences.