I was a lifelong PC girl until I got a laptop with Vista on it and wanted to hit it with a baseball bat almost every day. I cracked one day and went out and impulse-bought a MacBook Pro and I will never, ever, ever, EVER go back. The thing has been an absolute dream, almost zero learning curve to switch from PC to Mac and almost all the things I have to do are easier and more straightforward than on the PC. I also massively prefer iWork to Microsoft Office, and iWork allows you to save things in the Office formats so they can be opened on any PC if necessary. Newer Macs also have the capability to run Mac OS X and Windows XP simultaneously if there's some program that you use (usually business software or gaming) that for some reason doesn't have a Mac version. Apple is usually also rated very highly in customer service and reliability (I read an article before I bought, I think it was in PC World, that Apple had officially become the highest-rated computer manufacturer for customer satisfaction, which included reliability of hardware and helpfulness of service staff). They're also much less likely to be affected by viruses or other malware.
For the kind of apps I run and how I use my computer, a Mac is perfect for me, since the only apps I run besides normal web browsing and word processing are Adobe creative apps - Photoshop, InDesign, etc. Macs are industry standard in most creative fields, so those programs run exceptionally well on Macs.
Also, to the poster who asked - I wouldn't get a MacBook Air unless you're going to be constantly traveling and taking the computer with you in situations where a regularly-sized computer wouldn't be appropriate. If it's just going to be used like a regular laptop, save some money and get a regular MacBook. The disadvantages of the MacBook Air (lack of optical drive, few USB drives, etc) are a fair trade-off for some people that need extreme portability, but if you don't, they're not worth it.