I was actually looking for something completely different (a bit-bang USB device emulator for AVRs) when I came across this little bit of freeware: the AVR MacPack.
It’s not quite AVR Studio, but it sounds like it might make it a little less painful to set up a Mac for AVR development. I don’t currently own a Mac to try it out on, so if anyone does give it a shot please let us know what you think of it.
-Adam