I had the opportunity to try NX9 on a Mac the other day (running under 10.8). I have used Apple products since the Apple II in 1977, will always prefer to use Apple products where available and run everything in our shop on Macs and iPads except NX. The Mac implementation that I experienced the other day was truly awful, it could not be more unMac like if it tried.
No doubt Siemens will say that the numbers aren't there to warrant the investment in developing a true OSX application, but there's the rub - the numbers will never be there without a significantly improved user experience.
Until such time I will continue to use NX/Windows on Apple hardware