Differences:
* No viruses out in the wild for Macs for over 10 years now. Windows is riddled with them (well over a 114000 of them). Security by obscurity is a total myth. Windows Vista had 10,000 viruses while it was still in beta. Mac is inherently secure through its design.
* Macs are made by one company who makes both the Operating System and the Hardware. It all works seemlessly together. PCs can be made by many different companies. They don't always work well together and there are often conflicts that can crash the system outright.
* The Mac interface is designed so you only ever learn any aspect of it once. It works the same way across the operating system and in every program you use. There are also way more keyboard commands than on a PC.
* A Mac can run Windows either natively on a second hard drive partition or within the Mac OS itself using a virtual computer (Parallels or VMware software). Macs can also run Linux and other OSes in the much the same way. Mac OS X has a certified version of UNIX under the hood (based on FreeBSD UNIX) that is similar to Linux.
* Apple releases way more major versions of its operating system in the same time frame that Microsoft does theirs. When Apple updates the operating system it often becomes snappier and does more useful stuff. The last OS X snow leopard update doubled the gaming frame rates of the graphic system. With Windows you can expect it to need twice as much space as before and go half as fast. Most Windows updates are to fix problems caused by viruses.
* A mac is more durable than a PC. My last Mac (a G4 Powerbook laptop) was in constant use (24/7) for 7 years before I finally upgraded to a new IMac. It still works today. Windows PCs are lucky to last 2 years before they slow to a crawl and die a horrible death.
A mac is a premium product that is designed to last. The whole expensive debate is abit of a fib. Macs are priced competitively compared to PCs built to the same Specifications. I once read a report where a Mac Pro tower was compared to a Dell tower with similar configuration. The Mac was $1000 (USD) cheaper. Even so, even where a Mac is more expensive, it is better value for money.
I have used both PCs and Macs since the dawn of the PC age. I own two Macs and would never buy a PC ever again.