A post by id Software's Graeme Devine to the Quake3World.com seems to indicate that Mac Quake III Arena CD key authentication issues should be a thing of the past (thanks Matthew Riddle). Here's the poop:

Hey.

As of today there should be no more issues with the Mac authentication process. You do not have to download a patch.

If anyone is still having a Macintosh CD key problem please email me at zaphod@idsoftware.com and I'll do my best to get things resolved.

Graeme.