There's been some speculation that Apple could sell iPods with Mac OS X installed on the disk drive. Just plug the iPod into a PC with a USB/Firewire cable and boot up. The iPod would be the dongle.
If Apple's business ever slows down, they can easily release a generic version of Mac OS X and generate billions in fresh revenue. But the support costs would be higher, and the quality of the user experience wouldn't as good. I hope they won't ever need to go down that route, but it is good to have it as an available option, just in case.
I think selling a chip to quality motherboard manufacturers like Asus would be the way to go. Dell motherboards, at least at the low end, are such crap, that I wouldn’t want to be associated with them.