Can't resist:
Apple Certified Refurbished iBook G4 12-inch
Refurbished iBook G4 1.2GHz/ 256MB/ 30GB/ CD/ E/ 56K/ 12-inch TFT
• Save 23% off the original price
Original price: $899.00
Your price: $699.00
(Warranty is the same as a new unit). No need for antivirus; no problems with worms, trojans, etc. Support is available in person at the "Genius Bar" at any Apple store -- regardless of warranty coverage.
I've run my business on Macs for 18 years, and have often had PCs alongside them. I currently have a Dell with P4, 2.54 GHz. It was about $499 on special a couple of years back. That's without monitor, of course. It's about 20X more likely to crash or hang than the Mac.
Dell's reputation is that as long as it works, you're fine. If you need anything from them, ever, you can be in for a world of hurt. I had an acquaintance get his attorney involved in communicating with Dell and was ultimately able to get Dell to buy back their PC.
But anecdotes aren't that useful.
Here's a large study that looks to be about a year and a half old:
http://www.pcworld.com/reviews/article/0,aid,118514,pg,3,00.asp