When people ask me what kind of computer I use, I always give them two anwers. I tell them I use my PC for gaming, and my Mac for design. I switch off when doing other things, but when designing, Mac is the way to go.
The greatest thing about using a Mac when you’re designing a site, or even something else is the navigation between programs. It’s much more seemless to switch between programs when using a Mac computer. You can simply hide your current program, open a new one and switch off between the two very quick. With the PC, when you minimize it doesn’t seem to ever help in terms of memory. With a Mac, you save a lot more memory space by hiding programs than with a PC.
The screens on Mac computers are built more for designing as well. The screen that you’ll find on a Mac monitor is much more colorful and vibrant. When you open applications, the windows always seem to have much more space on a Mac than a PC as well. Most of this is due to the development companies, and not the computer. Still, you’ll find alot more use of real estate when you use a Mac.
About the only huge negative I’d give the Mac, is the standard abscene of the right mouse click. You can modify this, but out of the box a Mac doesn’t have a right mouse click. You have to hold down crtl+left mouse button to execute what would be a simple right mouse click on a PC. Again, this can be modified simply by using a two button mouse. So there really isn’t much harm in it.