It's a great piece of software. I maintain a few Macs for my family and they don't use Apple keyboards for various reasons. Since Apple refuses to add support for standard PC layouts (and creates monstrosities like localized keyboard layout which has @ key on shift + alt + 2 which causes no end of support requests), having Karabiner remap it to the standard PC keyboard layout matching the hardware is a huge boon.
System Preferences => Change Keyboard Type… gives an UI that directs you to press a few keys that help detect your keyboard layout. That has worked fine for me (N=1) when adding a Dell keyboard to a Mac Mini.
I think that UI was added for the Mac Mini, as it was the first Mac sold without keyboard ("bring your own keyboard and mouse")
