It has been revealed that Microsoft's Windows 8 Pro edition will allow customers to downgrade to an older version of Windows if you aren't entirely happy with the latest iteration. Users can elect to install Windows 7 or Windows Vista in place of the new OS although it's worth pointing out that you'll be without a boxed retail version should you go this route.
It seems unlikely that most buyers would want to downgrade but as Engadget points out, there are a few scenarios where having options would be plausible. Manufacturers could include a copy of Windows 7 along with new PC purchases in order to give shoppers more flexibility.
These same companies could also sell new computers with Windows 7 pre-installed in the event that some users wouldn't be comfortable spending money on a system with an OS they are unfamiliar with. A dual-boot option would be the perfect scenario for PC users to learn Windows 8 at their own pace but it's unlikely we will see this.
Downgrading to Windows 7 might also be an option in the event you are running mission-critical software that might not yet be fully compatible with Windows 8.
It's worth pointing out that Windows XP and earlier operating systems aren't included in the downgrade rights. Furthermore, the service is only offered on OEM copies of Windows 8 Pro - retail versions and other editions of Windows 8 need not apply. Windows 8 will be launching on October 26, 2012.