Jim covered it. I used Pc version for a long time, started the Mac beta a year or so ago. I use the Mac version exclusively now. It is a bit different, but only slightly. Most of the differences that you will notice in daily use are some keyboard shortcuts in the Mac version are different from the PC version. Every update they produce gets them closer to parity and development is very active.
I would rate it a good buy and I was glad to finally turn off my PC and go full Mac (other than a MacBook running win7 in Boot Camp for my Shopbot)
If you already have Rhino for Windows, you can get the Mac version at a substantial discount. If you participated in the beta tests and also own the Win version, the discount is insane- $95 for Rhino for Mac. It took about three seconds to decide on that purchase!
