Is it 'safe' to use FN for custom shortcuts I'd like to create my own shortcut combinations, and it looks to me that the fn key is actually only used for a few shortcuts on OS X. For example, fn-delete is forward delete. In applications like Photoshop it's not used.

Are you aware of any applications that uses fn shortcuts? I don't want to create potential conflicts. If feels strange to think that no software is using such a simple key, and they go for the more complex option-command-shift combinations instead.

Just to be clear, I'm referring to the use of the fn key (eg. the one usually on the lower left side of a MacBook Air's keyboard), not to the function keys (F1 to F19) found at the top of the keyboard.
You cannot create shortcuts using the fn key in the preferences pane (but you can assign Function keys f1, f2 etc.) 

The shortcuts interface will allow you to press fn + X for Cut etc, but only X is displayed as the shortcut, and pressing fn + X results in typing X not cutting.

Very annoying for people that switch between Windows and Mac keyboards, since the CTRL key on a Windows keyboard is where the fn key is on a Mac keyboads.