There seems to be a large amount of backlash directed towards Windows 8 due to the fact that it's new UI exists alongside the old Windows desktop. I must confess that I was slightly shocked myself to witness the context switch take place on the video, but I was shocked in a good way. Ironically, the reason why I think it's good to have a Windows desktop alongside a touch UI is based on the same reasoning as why I switched from Windows to OS X in the first place.
I am typing this right now on my latest generation MacBook Air. The reason why I switched to OS X was because it was the best of both worlds. I could have a Unix shell, Adobe products, as well be able to use XCode to develop iOS applications (which you can't do on Windows, but that is a separate issue). I could do everything Windows could and more. Analogously, choosing between Windows 8 and iOS for a casual user is very similar.
I also have an iPad 2 and an iPad before that. People, mostly family, are always very attracted to my iPad and frequently ask me if they should buy one to replace their existing aging laptop. My answer is always a resounding no. Were that to happen, they would inevitably call me and ask how to open Office documents, view flash websites, and do all the other countless things that an iPad is not suited for.
Windows 8 solves this problem. Sure, there will be an initial period where some apps will only be available in desktop form. But, at least there will be a less elegant way to do things that otherwise couldn't be done. Additionally, this will only result in low hanging fruit for developers. If the metro tiling interface takes off, consumers will prefer a metro based application and developers will build one. Similarly, Android's additional OS-level features (at the sake of battery life, some might say) are one of the reasons why I prefer it over iOS.
Another argument against Windows 8 is that of market and developer confusion. There is no market and developer confusion. Apple has already set the precedent. Consumers and developers both know what they want and what to build respectively. The capability is there and the developer who builds what the consumer wants will win.
Based on WP7's market performance, who knows what will happen. My argument here is not to say Windows 8 is a winner. It is simply to say that the the arguments against it are misguided. I, for one, would prefer to be able to do more than less. One thing that is certain, however, is that having more competitors and innovation in the mobile/touch landscape is a good thing.