EFi-X USB dongle simply let you turn your PC into a Mac OS X, you hust plug it into a internal USB, stick in an OS X install disc and it simply let you install OS X Leopard on your PC. According to Gizmodo, they’ve installed and managed to grab all the updates straight from Apple, including 10.5.5, so you don't have to hack OS X to run on a non-Apple hardware (typical Hackintosh). It runs beautifully, just like a real Mac Pro.
There’re, of course, rules you’ve to adhere to, as there tends to be when using black magic. The major one with EFiX, and its only real "catch," is that you have to use the supported hardware, not a very long list indeed. But outside of the Gigabyte motherboard requirement (reportedly some Asus boards using a P45 chipset also work), it's actually fairly generic. I just happened to have everything on the list.
Keep in mind, you're violating Apple's EULA if you install OS X on non-Apple hardware, even if you've legally paid for the operating system. But you can still probably put together a hackintosh complete with a licensed copy of OS X and a $165 EFi-X dongle for less than the price of an official Mac.