FunctionFlip is a great little Preference Pane that lets you use some function keys as function keys, while leaving other keys’ special features alone. This is great for Xcode 4 users, because Xcode 4’s default keyboard bindings map F6 to ‘step over" and F7 to “step into.” Because of this, I’ve enabled “Use all function keys as standard function keys” in System Preferences. It’s annoying, though, because I use the special keys a lot. I just don’t use them as much as I use the debug commands in Xcode.
I’ve now moved “step into” over to F5 in Xcode, and I’ve used FunctionFlip for making only F5 and F6 behave as normal function keys. The special behavior of those keys is to adjust the keyboard backlight brightness, and I never use that (but if I need to, it’s as simple as holding down the Fn key).
Now I have all of my common cases accessible without ever touching the Fn key. Great little tool.