The actual case I encountered that motivated me to whip this up was a system with a failing but not totally gone hard drive. No longer bootable. The system's owner (who shall go nameless, oh, and, "Hi, Mom!"), alas, had lost or misplaced the original boxes containing the orange product key stickers. Luckily, I was able to copy the %windir%\system32\config\software hive, load it with the registry editor, retrieve the digital product ID values, and use this tool to convert them to product keys.