Apple produces their own machines, so they pick and choose the hardware/software that comes from the factory. This enables them to ensure that all the components "play" well with each other, and because they only have to ensure compatibility with those components they select, their OS can load faster and run more efficiently. Windows-based PCs, on the other hand, are built by everyone under the son. Therefore, Windows has to try to make their OS operate under an infinite number of configurations. That means the OS takes longer to load and it generally has to do more processing than a Mac would to accomplish a comparable task. But, along with that comes greater flexibility. Windows is infinitely customizable, while Macs are generally limited by what Apple things you can/should be able to do. Apple designs Mac's features based on what the majority of average users want, and they make it as simple as possible to do those things. So, Macs are seen as more user-friendly and as the option for people who want their machines to "just work". They've also done a remarkable job of creating a cult-like following through tribe branding. They've created a Mac culture that makes people want to be a part of the brand, regardless of the merits of the product itself. It's just "cool" to use a Mac or an iPhone. There's nothing dramatically inherant to the Mac OS that makes them any immune to viruses. Most of the people who design viruses simply want to wreak maximum havoc, and so they target the OS that has the most users worldwide...Windows. I'm a tinkerer by nature, and, so, I'm not at all intimated by Windows and the possibility of having to "fix" problems. However, I haven't ever had a virus or any real problem with any of my Windows machines (knock on wood). Windows 95 and 98 had their share of annoyances, but since XP I've been problem-free, and I'm currently using a Vista 64-bit system. I've used both Windows and Mac, and performance-wise or UI-wise, I don't have a preference. I guess it comes down to cost for me, and I can get a souped-up Windows machine for a fraction of a comparable Mac. When I say "comparable Mac", I don't mean that it must have the exact specs, because Macs operate more efficiently, meaning that it can have less RAM or a slower processor, yet still perform as well as a PC with more RAM and a faster processor. Yet, that comparable Mac with "inferior" components still cost more than the souped-up PC. As for software, a lot of software now comes with both PC and Mac installations on the same disc. For a very small fee (I don't know why $10 is coming to mind) Adobe will replace your Windows software with Mac software. So, that shouldn't be a huge hurdle if you switch over to a Mac. However, there are programs I use that are available only for Windows, not Mac. While it's true that you can run Windows on a Mac and software can help you run Windows programs on a Mac, why bother with the trouble/expense, when Windows will just natively do what I need for cheaper?
In the end, I see this like the Canon vs Nikon debate; whatever you choose, you can't go wrong.