What is a hackintosh?In short, a hackintosh is a regular PC on which you install Mac OS X. The challenge is that not all hardware is supported, so there is some research to do ahead. You do not want to pay for a fancy graphics card that doesn't work with the OS.
Why?The "it just works" concept did not appeal to me very much. The main idea was to learn, and there is no better way for that than doing it yourself. (To be honest, the price of Apple's hardware helped me make that decision as well.)
Add that I enjoy doing the research and learning about all the new hardware finesses since the last time I built a computer (2005), plus that I appreciate to tackle a challenge.
My old computer was getting crippled and too loud to my taste. These are just further excuses for having fun building a new computer.
As for many decisions people make, I think that my guts just decided to do it, then found or invented seemingly rational reasons.