Google has a kill switch, and has used it in the past a few times without much if any complaint.  Apple has one in iOS, but to the best of my knowledge it has never been utilized.  The underlying idea of being able to kill apps that are malware in disguise is a valid and potentially valuable capability.  Think about how many people there are out there that do not take even the most basic precautions against viruses/malware.  Some people don't run any anti-virus/malware software at all, and there is also a significant number of people who never even update their OS, thus leaving them unnecessarily vulnerable.  So in that it could protect people against their own sloth, I think a remote kill switch could be a good thing.

However, there is no certainty that Microsoft is going to use it in a purely protective manner.  What happens if there is a dispute between Microsoft and an application developer, unrelated to security, and Microsoft decides to use their power to simply remove the application, along with associated data, from every machine in the World that is running Windows 8?  I do not like the thought of that at all.       

So in the end, I am rather conflicted about the clear benefits that could be provided by Microsoft having a remote kill switch for malware versus the requirement that I surrender control over my own machine to Microsoft and trust in the good will and judgment of the company.  That latter concern leaves me quite vexed, to be honest.