Edit: Another thing is... any Mac specific issues I should know regarding Ren'py?... It's better to know about those things before I mess up and break things...
The only thing I can tell (I don't have a PC to compare) is that when I open up RenPy, there is this weird thing that happens when I push the icon is that it just "sits" there, and you have to push it twice for RenPy to truly open (as well as any game you play on a Mac.)
Though it seems you've probably discovered this by now judging by the date of your post. And who knows, maybe it's just my computer.
Hope you enjoy your Mac. I really like most Apple products but I feel like their hardware--not software--has failed me more often than the PCs I used to have lying around. So backup diligently.
The other two things I can't stand about Apple (aside from being quite satisfied with everything else):
1) Lack of ability to customize simple OS things (godforbid you want to enlarge the font size of ical, for example)
2) The legions of Mac cultists whose sole mission in life seems to be telling you how perfect the products are, how visionary Steve Jobs was for picking the font size, and why in god's name would you want to change something like ical's font size...it's already perfect...and your eyes must be bad.
(I'm almost quoting here.)
Sorry, rant over. *Fans self.*
Sorry, ranting here. Anyways, have fun.