Microsoft is walking down a very dangerous path with Windows 8, dangerous for the user. They are trying to put restrictions on the x86 version with the UEFI, but fortunately, the online backlash managed to convince them to get manufacturers to offer a physical switch, so you can still install Linux or any other OS you want. Because they initially tried to make it so you can't install any other OS anymore even on x86 machines (the ones that come with Windows 8).
But on ARM, they won't even offer that option, which means they will make it impossible to install anything else but Windows 8 on those Windows 8 ARM machines. While this may not seem like a huge problem like now, and it's still possible that Microsoft will not have the same 90% market share it used to have on x86 computers, they might still get a big share of the market thanks to the Windows legacy.
This is worrying because it means in the future, there will be very few machines where you could install your own OS. The only more "open" hardware will be the one with Android, and even there you still have to worry about locked bootloaders right now, and although some manufacturers are starting to backtrack on that, or offer unlocking tools online, it may still not be enough.
Microsoft is saying that this is only for the safety of the users, but it's becoming pretty clear that they are taking advantage of these new technologies, that could indeed offer more security, to lock-in their users and block competition. If Microsoft really wanted, they could find a way, just like they did with the physical switch for the x86 machines, which they might not have proposed in the first place, if people didn't make a big deal out of it.
Their Market on ARM devices is also worrying, because they won't allow any kind of application that doesn't come through the Market, much like on iOS, and unlike Android, where you can still install apps from other sources. If Android somehow loses in the future to both Apple and Microsoft, we're looking at a future, where devices are very locked down and you're only allowed to use applications that they've already approved.
This could mean the end of being allowed to do whatever you want with your computer. I feel this is a very bad trend, and it should be stopped early, either by convince Microsoft to not go that route, or simply voting with your wallet, and choosing open Android alternatives versus locked down Microsoft-vetted devices.