I don't think it was really designed to thwart the person who accidentally bought a Windows 7 Upgrade key but did a clean install so Windows wouldn't accept the key and the dude had to go get a crack.

This is for more like hardware. Think of it as x64 digital signatures except on hardware not software and Microsoft controls who has the correct signature and who doesn't. Even if you disable it though the BIOS, there really isn't a guarantee that all hardware would work correctly under a different OS.

Why it’s controversial

Many computer hobbyists, especially those who are fans of Linux, are not happy with the way Microsoft is implementing Secure Boot in Windows 8. There are numerous blog posts proclaiming the danger that Secure Boot poses to free/open source software. There is a Facebook group called “Stop the Windows 8 secure boot implementation.”

Their complaints are that 1) Microsoft will require hardware vendors to enable Secure Boot on machines in order to obtain the Windows 8 compatibility logo and 2) Microsoft is leaving it up to the hardware vendors as to whether the user will be able to disable the feature, and whether/what other operating system certificates will be installed in the firmware.

The problem (for those who want to install a different OS) comes when a vendor doesn’t provide a way to disable Secure Boot in the Setup menu and doesn’t install certificates for any OS other than Windows. In that case, those who buy the computers won’t be able to install Linux, either in a dual boot configuration or by formatting and replacing Windows with it. This possible narrowing of choices has the Free Software Foundation soliciting signatures for a petition to urge computer makers to provide a way for users to disable Secure Boot and/or install an alternative OS with Secure Boot enabled.
http://www.windowsecurity.com/articl...s-mean-IT.html