Choose the right tool for the job
I think you have to look at this from an objective point of view. Basically, it all comes down to what sort of thing you want to be able to do (specifically the software that you need to run) and the environment that you need to run your computer in. While I'd advocate a Mac for pretty much everything these days since I swtiched almost 2-years ago, there are some things that the Mac isn't great at. As far as my experiences go, I can list the following problems:
1. Games. If you want to play the latest games and you like PC-style games, then a PC is the way to go. You tend to get a faster gaming machine for your money and are guaranteed to be able to play the latest PC games. The Macs are generally under-powered for what you pay for them and the number of games isn't great, although it appears to be an improving situation. For example, both id and Epic appear to support the Mac for their game engines so as well as the likes of Doom 3 and Unreal we can also look forwards to games based on their engines. Bit of a shame that there's unlikely to be a Half-Life 2 but you can't have everything...
2. Windows-only Applications. While the Mac has a great selection of software, the specific software that you need might only be available for a PC. Do your research to see if what you need is available for the Mac as well as the PC and that it'll do what you need. I usually do OK but I still find myself using a PC for desktop database work since Office 2004 for the Mac doesn't ship with an equivalent to Access and I have a lot of databases in that format already. I believe that I could port them to something like FileMaker or MySQL but it'd be less convenient.
3. IE 6-only Web Sites. This is a particular problem in an enterprise environment where corporate web application require IE 6 to be used. Sometimes you can get around this with Firefox and setting it to maskarade as IE 6 but it doesn't always work. For example, my company makes heavy use of PeopleSoft 8 and this doesn't seem to work on anything but IE 6, although it beats me why. This is less of a problem at home where you have choice but it might be that, for example, your online banking software needs IE. I really hate that but it sometimes happens still.
Problems 2 and 3 can generally be overcome with, at the extreme, an installation of VirtualPC. However, if gaming is your primary objective then VirtualPC won't help and a PC would be your better choice. At the present time, however, I'm more inclined to suggest buying a cheap XBox or PlayStation 2 if gaming is your thing and still buy another Mac.
Basically, OS X is a wonderful OS and I'd recommend a Mac over a PC any day of the week assuming that it is possible that it can do what you need it to do. The ease of use, security and reliability make this a complete no-brainer. However, if you can't do what you need on Mac then it's hard to sincerely recommend it.
Not sure if that helped at all...