I was also a photographer and did all my work in the PC. Windows XP/Windows vista has never given me a problem. The only problem I've had were not related to the software itself but to a set of faulty ram.
My friend owned a new 2005 BMW 330 or something like that. One day while ordering food through McDonald's drive through the transmission gave out. Took it to the dealer and had it fixed. Turned around and sold his car and got a Lexus. Just because it's considered luxury doesn't mean it's good quality. Maybe his car was just a dud. I also found that his car was somewhat small. It felt like I was inside a Honda Civic only at twice or three times the price. It was a nice car but too expensive for my taste. These days I drive an Odyssey which fits my need for transporting the family around. It's no BMW X5 but it fits my need and my budget.
I am very glad to hear you can run XP for your photography: I have actually seen more pros switch to PC so they can invest more on photo gear.
For me, it's part of my workflow: I started using Photoshop in College on a Mac, at the same time I started my theater career with lighting software that only ran on Macs... Now, I design theater productions using a program called QLab, which will never be available for Windows. It also has to do with software licensing: VectorWorks is a cornerstone of my work, as much as the Adobe CS 3 Premium package.
It all comes down to familiarity, and quality for me. Yes, I have had hardware issues with my Macs over the years, but compared to the headaches I have seen my friends go through, it is minimal.
Now, about the BMW... wow. Okay, I do not want to offend any 3-Series owners, but a 3-series is basically the iBook of BMW's: it is NOT their best product just like the iBook was not Apple's best product. I would never buy one. For me, the 5 series has always been the quintessential BMW: the 7 series are for old farts, the roadsters are for old dudes who lust after younger women, and the X5 is for people who really should have bought an American SUV or a Honda.
I own an e39 540i/6 M-Sport. Jet Black. BMW's best car was really the 1997-2003 5 series. After 2003, the design went horribly wrong. Some lesser-educated BMW owners feel that because they own an expensive car, they can drive it without maintenance: big mistake: if you properly maintain a BMW it will run for many years without costly repairs...
Kind of like my Macs over the years: if you see your Mac as a finely-crafted machine (like a BMW) which needs upkeep, you will be rewarded with a positive experience.
The point is to take care of your investments: I have seen friends hose their Macs through negligence: physical and software-wise... and have fixed some of them. I have also had a girlfriend kill one of my BMW's by putting diesel in it. Everything is relative.
Okay, this is long-winded. I guess I'm a Mac and BMW e39 snob that takes care of his stuff.
The Microsoft ad is irrelevant to me. People who buy PC's will continue to do so. I will continue to buy Apple computers and one the right opportunity arises I will pick up a 2003 M5. Done.