Oh d@mmit Bobby...it's a good thing this is a pilot's message board. Hopefully the discussion won't get too out of hand!
Here's my take, as I use both. For 99% of computer users out there, the Mac has whatever software one would need. Especially now that OS X is there and all the UNIX software is available, typically finding a tool you need on the Mac is a non-issue. The most notable exceptions are games, and perhaps relevant to us - MS Flight Simulator is not available on the Mac. However for flight sim purposes, I'd recommend X-Plane anyway, which IS available. So on this front, you have to look at what you think you'll need, and make sure the Mac can deal with it.
OS X vs. Windows XP. From a technical stadpoint, both are pretty solid OS's that "shouldn't" crash. People that are used to the PC tend to prefer Windows, and vice versa. I find this argument to be similar to a "high wing vs. low wing" argument. There's a intangible element of personal taste that just can't be argued. I use both OS's extensively on a daily basis, and when all is said and done, one isn't
substantially more productive or better than the other. I do think OS X is a bit easier to use - mainly in the sense that it's better at dealing with new hardware, and apps tend to be easier to install, and especially, uninstall (remember that discussion about AOL before the boards died?).
Hardware - especially in the last couple of years, the PC is ahead. Regardless of whether you like the asthetic look and design of the Macs - Intel has run away from Motorola in the past couple of years. Apple is using dual processor Macs to combat it, but when you consider 533 MHz busses on the PC and 3.x GHz processor speeds, Apple has been lagging behind. Now this "isn't" a huge issue for most people. Only the most hardcore gamers that are counting FPS in Quake or something are going to notice the difference between a 3.4 GHz P4 and dual 1.43 MHz G4. The hardware has so completely outpaced the software in recent years, the vast majority of users don't use software that takes advantage of the speed. Even graphic designers and artists using tools like Photoshop don't care. I have a 2.6 GHz PC, and it feels essentially the same as my 1.0 GHz G4.
Odds and ends - the main reason I own a Mac is my iBook. The thing about Intel is that their philosophy in building chips pretty much boils down to stuffing more and more transistors into a small space, and deepening the pipelines to produce higher GHz yields. Higher GHz numbers makes for better marketing, but they're sacrificing efficiency and low power consumption to do it. Therefore you'll find that Mac notebooks tend to have better battery life than Intel counterparts. I get a good 4.5 hours of life with normal usage out of my iBook. My Dell for work gets less than half that. I figured that battery life was worth some of the advantages I'd get by having a PC (i.e. games), and picked the 'Book. I haven't been disappointed so far. But obviously power consumption isn't going to be an issue for you if you're not getting a portable.
Finally, it comes down to price. You'll find that Apple prices their computers pretty competatively with Dell's fully featured systems. That said, you won't find a bargain basement system for Apple - they don't have one. So if you're looking at a low end Dell with a Celeron processor for around $600, there's no Apple equivalent. Also, on the PC - you can build your own system and severely undercut Apple's prices if you choose. But then you'd miss out on warranty, etc..
So anyway, there are some things to think about. After using both pretty heavily for awhile, I find that there's really not nearly as much difference as the "Macs suck!" and "PC's suck!" camps would like you to believe. Usually the guys on both sides of the fence that unilaterally say, "XXX sucks!" are FOS. You may need to bring both a Mac and PC home and just see what feels right. Then bring the other back at the end of 30 days.