I personally don't know any Mac users that run Windows stuff in emulation on their Macs. You can using VirtualPC but being that it is emulation it is really slow. For the same price as VitualPC you can just buy a really cheap PC box.
Macs run
Mac OS X these days. They can also run all the older Mac Classic software in the Classic environment and Linux software in the X11 environment. Both of these are not emulators and are just as fast as the Mac OS X environment. Also you can just open up Terminal for those *nix people who "don't understand why the mouse was invented when it just takes your hand off of the perfectly good input device known as the keyboard."
For non lovers of the unix command line like myself you can use Fink to install unix applications like Gimp and Open Office.
http://fink.sourceforge.net/
http://finkcommander.sourceforge.net/about/#screenshots
http://gimp.org/screenshots/macosx_screenshot1.png
Macs also come with Apache, MySQL, PHP, and all much of the other common *nix stuff that you find on your web server installed and ready to run right out of the box.
http://www.apple.com/macosx/features/unix/