Until you replace your motherboard or get a new BIOS.
Hence my statement "in the vast majority of cases." Unless, of course, you're implying that replacing your motherboard is a frequent occurrence. I've never had a problem with BIOS upgrades in terms of activation.
Seeing as the motherboard is the most basic (and least likely to be replaced) component of a computer, replacing it makes it seem to the software that it's on a different machine.
actual i got tagged on xp for a harddrive change on an oem box.