I’m currently using Mac OS X on my MacBook Pro to do most of my day to day work. There are some people out there using Mac OS for Openmoko development. But there are lot more resources for Linux. Furthermore I’m more familiar with development on Linux than I am on Mac OS.
Using USB networking is straight forward just plug it in if not automatically done connect the usb device to your Virtual Machine and your Debian will recognize it.
The Only thing I could not yet get working is the USB port to flash the Freerunner. Debian always prints an error. I try to find a solution for that.