Until ProntoEdit comes out I can't be sure, but I think that if you have a PC emulator like VirtualPC or SoftWindows and a COM to Serial port adaptor than using ProntoEdit on a Mac should be as easy as on a PC.
For example I have a Palmpilot with the MacPac and a Mac with VirtualPC. I can HotSync the palmpilot on the mac desktop or on the windows desktop no problem, all from the same computer.