Microsoft is planning to implement the UEFI OS-booting system in Windows 8, which is fine. What's not very fine at all is that it'll be locking out other operating systems from the ARM version, meaning Windows 8 tablets won't be able to run anything else.
According to the Software Freedom Law Center, Microsoft has confirmed that the "Custom Mode" required to boot alternate operating systems has been prohibited in Windows 8 when it's running on an ARM device. This means the only boot option will be Standard Mode -- Windows 8.
Those running Intel machines will have the option to completely disable all boot locking entirely, but that won't be possible on ARM devices. Windows 8 tablets based around ARM chipsets will only be able to run Windows 8. [SFLC]