After two days of consistent use, APEX on OS X has performed flawlessly! And it's fast - REALLY fast! Sure, there's no network there to slow things down, but when using Safari 4, it's just as fast as static pages!
Now that Oracle runs natively on OS X, I can stop relying on VMs for that service, and use SQL Developer, Firefox and other Mac tools for 100% of my development.
I just hope that the folks at Oracle make this a supported configuration at some point so that we don't have to keep running in an unsupported fashion.