Of course this isn't strictly true as the article mentions how people got confused with "double desktops" but given the rest of the article, it just seemed like people were forced to use apps that they otherwise wouldn't have used and thus gave plenty of complaints.
For example, his section on multiple windows seemed bizarre to me. Yes it is true that Metro does not support multiple windows but to say that Windows no longer supports them is simply incorrect. If a user wants to "collect, compare and choose" among multiple web pages then they can easily do that as they always have through the desktop. I think the important question here is "were they unable to find the desktop" or "were they told to only use Metro browsers"?
I think we should have faith in users to choose the correct tools for the task. Forcing them to do something the arguably "incorrect" way simply to have them struggle seems to simply be a self fulfilling prophesy.
And hey - I think a study proving that Metro on the desktop is less than ideal is perfectly okay. In fact I'd say I probably agree most of the time. But to label this study as Windows 8 as a whole as opposed to simply metro on a desktop I think is a little unfair.
Many of the arguments I find come from people forcing new users to only use the Metro style UI, which would obviously be confusing (much as my mother would have problems switch from a PC to a Mac).
I'm sure people will praise windows 9 for being so much better than windows 8, even though windows 8 took all the risk and windows 9 simply applied some polish.
Whether you like it or not, you will likely be using Metro apps on a regular basis in a year or two.
But the people in the usability study were no power users. They were the intended audience. Besides, I don't think the performance issues OP describes would be appreciated by non-power users either.