Does upgrading to Windows 7 deactivates the license key for any prior version of Windows?

For many people, one of the reasons holding them back from taking the plunge for Windows 7, is the fear of the unknown and the general belief that upgrading to Windows 7 would prevent them from coming back to whatever previous version they owned. The true of the matter is that this is just not the case: owners of previous versions of Windows can always go back to that version if they are not happy with Windows 7 after trying it out, without losing the product key of the of their old versions.