There are some issues that might be handled differently when using an Arduino Leonardo. Details are available on the Arduino Leonardo Page.
The first difference we saw was in programming it the first time. When we removed the device from the Mac and reinstalled it, the Mac popped up a dialog asking to setup the keyboard. What? That is one of the differences. Until you invoke the bootloader, it looks like a keyboard or mouse to the computer. The bootloader creates a virtual com port, uploads the data, then uses it for normal serial monitor traffic. Resetting the Leonardo tears down the virtual port, leaving you with a normal HID device. It generally doesn't matter, but the first time the computer sees the Leonardo, it will throw up the dialog.
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