Microsoft have responded  to suggestions that Windows 8 may make it difficult to boot alternative operating systems. What's interesting is that at no point do they contradict anything I've said. As things stand, Windows 8 certified systems will make it either more difficult or impossible to install alternative operating systems. But let's have some more background.
We became aware of this issue in early August. Since then, we at Red Hat have been discussing the problem with other Linux vendors, hardware vendors and BIOS vendors. We've been making sure that we understood the ramifications of the policy in order to avoid saying anything that wasn't backed up by facts. These are the facts:
* Windows 8 certification requires that hardware ship with UEFI secure boot enabled.
* Windows 8 certification does not require that the user be able to disable UEFI secure boot, and we've already been informed by hardware vendors that some hardware will not have this option.
* Windows 8 certification does not require that the system ship with any keys other than Microsoft's.
* A system that ships with UEFI secure boot enabled and only includes Microsoft's signing keys will only securely boot Microsoft operating systems.
More here 
An obvious question is why Linux doesn't support UEFI secure booting. Let's ignore the issues of key distribution and the GPL and all of those things, and instead just focus on what would be required. There's two components - the signed binary and the authenticated variables.