I have to make IT purchase decisions for a 3,000+ employee education organization, so the PC vs Mac issue is always on my mind. And I own machines from both platforms, an use them both on a daily basis. Here's some observations:
1. The platforms are actually converging in terms of feel and features, pretty rapidly. It seems like Microsoft adopts what it likes about the Mac when it updates Windows, and Apple does the converse. (For example, as far as I'm concerned, the new taskbar in W7 is actually better than the OSX dock, but I suppose that's a personal choice. Let's see what we get in the next major rev of their OS.)
2. I get the feeling that Apple is steadily moving mainstream/consumer with their product line. While that does get them more market share, it also leads to problems for some of their previous target groups, like serious photographers. I'm thinking here of glossy laptop screens that don't dim well, and color management pipelines that get dumbed down for the masses. In the mean time, Microsoft steadily improves Windows color management. So in another five years, I'm not sure they'll be all that different for our purposes.
3. There's a tendency among the Mac faithful to go full Apple. They'll buy a Mac, an iPhone, and an iPod, and eschew Microsoft forever. That sure makes integrating all of their devices easier, but those kinds of owners will sometimes miss out on developments in the PC world. Even in this thread, we have people comparing Snow Leopard to XP, which is like comparing a new Windows 7 machine to an early Mac G4. Windows 7 really is very good, Apple's snarky "I'm a Mac" commercials notwithstanding. XP is still in use all over the place, but none of my personal machines are running it now. I have a copy of the XP Virtual Machine running in Windows 7 Ultimate on my fastest home computer for, you guessed it, making prints for custom profiles, since Snow Leopard is troublesome, and the Windows 7 printer drivers for my 5 year old printers don't include an option to turn off color management.
4. The Apple hardware is substantially more expensive. It tends to be of high quality, especially in terms of design and feel, but there's no getting around the fact that you can just about always buy a faster PC for less money. My mother has a beautiful HP touchscreen all-in-one (running Windows 7 now) that she got just a couple months ago for $600. I've never seen an iMac for anything close to that. Having said that, I just ordered a new MacBook Pro, because I needed a laptop that could run on battery power for many hours while I'm in meetings. Initial purchase price is one factor, but repairing Macs is usually much more expensive than PCs. Mostly because Apple doesn't want you taking them apart, and goes out of the way to make that difficult and expensive. It's sort of like the auto world: You can buy an inexpensive car that is cheap to maintain, yet somewhat unreliable, or you can buy an expensive car that rarely breaks. Good arguments can be made in either direction. There are inexpensive cars that are very reliable, but nothing quite like that in the computing world. Maybe an Ubuntu laptop I guess.
5. Apple spends a lot of resources really trying to figure out how their users work, then they design their h/w and s/w so that it works as smoothly as possible in that context only. That is great for the majority of users, but not so great for the minority with special needs, or an interest in tweaking. I'm told that they stuck with one-button mice for so long because research told them it was the best way to prevent a user from using the wrong button. Great. There are those of us who mastered multi-button pucks during the Reagan administration, and don't need uncle Steve looking after us in that way. But for many people, computing simplicity is a godsend.
6. The real question is where we'll be in ten years. Cloud computing and software as a service could result in the OS being pretty much irrelevant. We'll just have to see. In the mean time, if Adobe would publish Linux versions of Lightroom and Photoshop, I can tell you where I'd start spending my money...
7. Let's start arguing over the best pickup trucks - that's just as productive as the classic Mac-PC argument.