You are violating Apple's EULA agreement if you attempt to install OS X on non-Apple branded hardware.
The legality of this "EULA violation" would possibly have been cleared up in this court case. However if the case is terminated then Apple's EULA still stands as a valid contract with the purchaser.
I think the principle area of dispute stems from the definition of the OS. Is the OS an integral part of the entire product? Or is the OS just another piece of software?
If you feel that the OS is integral to the product then Apple has a valid claim to tie the OS to only their hardware, because it directly affects the user experience and Apple has the right to control that experience.
If you think that the OS is only software and that once you purchase the software and if you can install it on any hardware, then it should be your choice as to what hardware you use, not Apple's. Apple is not required to support the hardware that you choose, but Apple should not be able to make it unlawful if you choose to install the software on alternate hardware.
These are the two principle camps and the courts apparently are not going to decide the issue.
Thanks for the very informative reply! I wasn't aware of the exact EULA. That being the case, I really would have liked to see this cleared up in court.
Say, for instance, that my motherboard went bad on my mac and I replace it and re-install (a legal copy of) OSX, would that fall under "non apple-branded hardware"? ... seems like some area for debate there...