From time to time you will want to reinstall you os right? And of course you have all your license keys documented right?
Well, I don’t 
Thats why I usually extract them from my computer before i reinstall the os.
A nice little tool that I have been using for this is ProduKey.
It has a small footprint, no need for installation, just run the exe file.
It gathers your licensekeys for windows, office, exchange, sql etc. And also have some features for gathering keys from across a network.