I've been a longtime Mac user since my start in Graphic Design back in the early 90's. I've purchased (on average) a new, Pro Mac every year since 1994. Actually, it's probably more than that (what can I say, I like to keep my machines new, it's a curse...).
Since 1999 I have been forced into using PCs at my day job (I'm a web designer). Back in 99 it was on NT4. While NT4 didn't have anything on the Mac in terms of interface and usability, it did have a solid foundation and it was rock solid, something that OS 9 wasn't.
When Windows2000 came out, I deemed it good enough to justify putting together a franken PC and using a Wintel box to get some work done that couldn't be done on the Mac.
I've just bought my first "real" PC, meaning, a PC that I actually built with the intention of it being a serious workstation, not just a helper machine to my Mac (which is now a QS 800 DP).
I've now had a month with XP, and while I still prefer most of OS X to it, it does narrow the usability gap, and does some things right that the Mac does wrong.
XP's low level system has a huge leg up on OS X in maturity. Simply put, in XP, I NEVER get an hourglass spinning when doing mundane tasks like navigating through the system. Keep in mind my XP machine has 512MB of RAM, whereas my G4 has 1.5GB, and is still plagued by random spinning cursor of death outbreaks.
Lightwave runs much better on the PC (again, with 1/3rd the RAM and a much weaker GPU than the G4).
However, OS X is still a heck of a lot easier to use than XP. The iApps trounce anything MS includes with XP, or is available in commercially for that matter.
As MacLuv states, XPs help system is better than OS Xs (why is OS X's help system SO slow?). But of course, under OS X, you shouldn't need to use the help section that much, because it is easier to use.
OS X is designed to be intuitive and logical. XP is completely illogical, but provides built in Wizards that simplify the tasks as best they can.
Another thing that completely IRKs me about XP (and just about every Windows flavor) is that there is no enforcement of common key commands for repeated tasks. Sure, most apps use CNTRL X, C, and V for cut, copy and paste. But what about CNTRL W for close window? Hell, even Microsoft can't standardize this within it's own apps (Outlook still doesn't recognize it).
Bottom line, both machines are nothing more than tools. The Mac isn't always the best tool for every job, ditto for the PC. I'm glad I was finally able to quell the RDF, put away the koolaid, and think CLEARLY and see that true nirvanna is a mixed environment.
Heck, I might even get me a Linux box...