I found a nice interesting article over at macobserver.com detailing a panel discussion at this year's South by Southwest (SxSW) Interactive festival called "Behind the Scenes: Developing OS X and Longhorn." Two former user interface designers at Apple and Microsoft talked about the design considerations that have gone into Mac OS X and Windows XP/Vista.

Cordell Ratzlaff, a nine-year Apple veteran, was head of Apple's human interface group during the time Apple acquired NeXT and began developing Mac OS X. Mark Ligameri spent six years at Microsoft working as a designer on Windows XP and Vista, as well Office 12 and other Microsoft projects.