I use a Mac and was also pretty worried about this before I bought my GP32.
I use a SMC reader rather than software and that is really excellent for the job so I'm more than happy. I'm not a coder so I'm unsure about development on a Mac, but OSX is closer to UNIX so I assume there would be all manner of possibilites, and there's always Virtual PC when necessary...
What I really want for my Mac is a decent Amiga emulator, the PC has had more than one for ages, but Mac UAE is stuck in the doldrums...
®