Information design hero Edward Tufte has some thoughts on Mac OS X:
The OS X interface design is distracting and self-conscious, with a marketing slickness rather the straight-forward transparent charming style of the past. It is out of tune with the superb industrial design of Apple hardware. Mac users will probably get used to it.
For my own current work (Photoshop, Illustrator, Quark with large files on large monitors), I see no particular reason to prefer the new design to 9.04. Indeed I regard 9.04 as nearly ideal (large flat-screen monitors are key; the Apple Cinema monitor is an enormous advance in design and as a working tool). Maybe when we do digital video that will make a difference in favor of OS X.