I'm amazed at the lengths people will go in order to defend a corporation which is only interested in making money and has no ethical or moral obligations whatsoever.
OEM license has never been tested in court AFAIK (please correct me if not), so don't act like your opinion is the true fact and only correct opinion. Until proven valid in court, OEM license is just a piece of paper. Also, breaking a license agreement isn't the same as breaking a law, so don't ever call it "illegal".
While I try to be fair to Microsoft and other software makers, some of the restrictions and rules are simply contradictory and/or nonsensical.
OEM license is tied to a pice of hardware, sure I can buy that. But I can't see how they can prevent you from changing your motherboard. As you and others have pointed out, it *IS* acceptable to change motherboards in a "warranty" repair. Who provides the warranty of a computer? The manufacturer. If you are building your own PC, YOU are the manufacturer. Any change you want to make to that PC can be qualified as "warranty" repair, if you want, so you can basically change the motherboard at will, IMO, if you built the computer yourself and used an OEM license.
That said, any other part of the computer can be replaced as well. You can justify it all the same way, so ultimately my opinion is that as long as you aren't using an OEM copy on two different computers at the same time, it's fine, regardless of any scary lawyer language in the license agreement. If Microsoft asks about my motherboard change, it was done UNDER WARRANTY, as it was, and as such is within the restrictions of the license.