Unmodified F4 no longer summons LaunchPad
One solution is to rm ~/Library/Preferences/com.apple.symbolichotkeys.plist and log out and back in. I just tried this and it seems to have restored the binding, no hack like FunctionFlip required. My other special keys all work, too. However, I lost my other customized Keyboard Shortcuts, like ctrl+&#x2190; for switching spaces Mission Control. They worked after I re-enabled them.

It looks like com.apple.symbolichotkeys.plist is the preferences file, and MacOS works fine if it's missing. After I'd edited my Keyboard Shortcuts via the preferences panel that file was recreated and everything's back to normal except Launchpad launches again. Based on a diff of the two plist files I'm guessing the keycode for Launchpad is one of 118, 119, 64, or 65.

I found this solution on a MacRumors discussion.