Apple's Mac OS X gets better all the time. Going back to the "classic" Mac OS feels less and less appealing every time I do it, so I do it less often. And in almost every way, the current Mac OS kicks Windows XP's butt all over the place.
However, Jon Siracusa's excellent (as always) review of Mac OS X 10.3 "Panther" nails it (as always) with respect to the broken way the Finder now works. I don't know anyone who isn't sometimes (or often) confused by the way windows and file management now work on the Mac—because Apple has fundamentally broken the spatial metaphor that made the original Mac Finder so intuitive for nearly 20 years:
[In] the classic Mac OS Finder [...] there is no complex set of rules to be memorized, no strange mechanisms to understand, absolutely no "game" to be played at all. There is no 14,000 word treatise on the user actions that determine the subsequent state of windows in the classic Mac OS Finder. I doubt anyone even thought about the issue at all. Everything is always how you left it. What's to know?
It's a pity that such great simplicity, so well executed back in 1984, has been lost and not (yet) recovered among all the yummy things in the new operating system. Worse yet, it wastes my time almost every day.