@winlux
Come on man you cant bring a SGI Machine into this conversation. Thats like comparing God to a human. I would kill(no i wont) for a SGI. You my friend know good stuff -=)
@HomerJ
Very good points.
Yeah, the truth is that the things best-suited to specialized applications (graphics, servers, etc) are not available to you or I.
For graphics, Macs and standard x86 PCs are pretty much equivalent. Some PCs will be better than some Macs, some Macs will be better than some PCs. The ones that will be better are simply the most recent ones, regardless of whether they are Apple or not. Obviously, high-end SGIs are the best, but chances are no one here can afford one.
For servers, non-Macs are probably a little better, since they generally have more memory and can take more modification (adding more hard drives, memory, other upgrades). However, a high-end SPARC machine is probably best-suited to this. Good luck buying one, they can cost more than most people earn in their whole lifetime. If you're gonna go for a cheap SPARC, don't. Just build your own PC far cheaper and better. For a low-end server, non-Apple x86s are probably best, seeing as they are the most cost-effective while still allowing for some real power.
Macs and PCs are just cheap, low-end hardware when compared to what's out there. However, they both use the same hardware now, and non-Mac PCs are much cheaper and more upgradeable. So, I would go for a PC.