The usual answer to this type of switch question is that it depends on what you plan to do with the computer and how much money you have.
For staying with a PC, the two biggest pro-pc arguments are cost and compatability. There is little doubt that PCs are inherently cheaper (although Mac fans will debate the quality of hardware versus cost) because the hardware is cheaper. There are plenty of hardware makers, so there are tons of choices which leads to lower costs. You also have a wide variety of programs and since the majority of people and businesses use PCs, there are less compatability issues. You will also be more likely to find software you need (whether they are games or business programs). If you're already in the PC camp, then you won't have to deal with learning a new system, which despite Apple's claims can be a bit annoying. Vista looks good and has promise, but it isn't quite there yet.
For switching, you're going to have to spend more money. You'll have a more costly time upgrading your hardware, but Macs tend to hold their value much longer than PCs. OS X is a very good operating system, and iLife and iWork are excellent program suites with cool features. Experts generally agree that Macs are superior for doing intensive photo and movie work, but suffer a bit in the games, business, and accounting software areas. However, thanks to Apple Bootcamp and Parallels, you can run Windows XP and Windows Applications from your Mac. Macs also have much less to worry about from viruses and spyware. With the impending arrival of Apple TV, I think we may see the arrival of a Mac media center system in the near future with full DVR ability.
In short, go to a library or Apple store (or reseller) and play with a Mac. See if you like it. Buy a used or refurbished one for cheap and give it a try. It is very difficult to make this kind of decision without researching and testing it for yourself.
