This came up as a possible solution in my other question, as a low-tech to ID a PC using registry values. It seemed worth its own question: what keys/values can you be sure won't change (barring re-install or major hardware changes)? Does Windows itself generate any GUIDs or anything like that which can be accessed - Windows is able to detect if you clone it to another PC, and ask for reactivation, I think - does any of this get exposed through the registry? Registry is an attractive option since it doesn't require learning any new libraries or APIs, and also our wxWidgets app doesn't use Win32 right now but wx does ahve registry functionality.
So far SOFTWARE\Microsoft\Windows NT\CurrentVersion\ProductID was sugested, what else? I noticed there is a key called SOFTWARE\Microsoft\Cryptography\MachineGuid...