I've always used PC. My dad began his career as a programmer in the early 90's and I spent much of my time on the various systems we had. Only used Mac's in high school.
Why can I not choose both? I own a PC and a Macbook Pro. At work I am using only PC, at home I am using both (PC mostly for surfing and gaming, MacBook for RPG writing and as my "media player")
I really like the Mac's 'ease of use' factor, but until a Mac can give me the versatility of a PC with regard to hardware customization, I'll never own one.
I like computer games, so I've always used a PC. After something like fifteen years using "IBM-compatible" machines, I find the Mac interface really awkward and annoying when I have to hop on the one we have at work. I don't see myself switching ever.