Larry Osterman (ya, the same Larry Osterman that got bit by the Audio bug) has a great post on why XGL isn't as useful as Chris Pirillo thinks it is. Can you imagine the tech support calls from the receptionist at XYZ Paper Company in Diluth, complaining that her app keeps crashing when it's really on the other side of the "desktop cube"?
I've said it before, and I'll say it again: OS X can afford to take creative liberties with it's OS' visual stylings because a) most of its users are right-brained creative types that value visual appearance over usefulness, b) its userbase is so small that drastic changes only have minimal overall impact, and c) even fewer businesses rely on Macs, so the retraining issues there are minimal as well.
The bottom line is, pretty does not always equal practical. Plus, Microsoft has other considerations, like the financial impact of UI changes on companies adopting their software. (Too bad calculating this impact is not as simple as it was in 1995). The Windows UI is the victim of Microsoft's monopoly success on the desktop, plain and simple.
I would think that, being a savvy businessman, Chris would understand this. Personally, I think Chris has a lot of valuable things to say (and while singling out Chris, I'm also speaking to other UI detractors as well). As well founded as his UI gripes may be, his feedback on Vista would be far more valuable if he accepted the reality of the situation and focused on problems that actually stand a chance of getting fixed at this point in the game. Acknowledging the fact that Microsoft has made huge strides in the fit & finish department might also be appropriate.