I use a laptop most of my time on a computer. I have a home laptop, and a work laptop... and in neither case would I want them to be touch screens. And for the record, I have used MANY touch screens in my career including the Surface, iPad, phones etc.
While I use my laptops as portable computing devices, more often than not (I'd say 90% of the time in fact) they are sitting in docking stations or attached in such a way that my 24" monitors (at work) are some 3 feet from my head. I don't have arms like an orang-utan, so in order to use these effectively as touch screens I would either have to move WAY closer (which then would require an awful lot of head motion with monitors that size) or indeed get smaller monitors. But then there's the eyestrain factor. I sit that far from my monitors because I have found it comfortable on my eyes. If I were to use the Metro start screen as my start menu, then every time I launched a new program I would have to sit up, lean forward, operate the menu and then lean back to my comfortable position with my hands on my keyboard to type. How is this better than the mouse that is FAR closer than my screen (being right next to my keyboard)?
To take this even further, when working on my laptop as I am this exact second, I sit about 2 feet from my 14" screen with my hands resting comfortably on the keyboard. If I want to use the mouse it is about 6" to the right of my right hand... lovely. Or I can just reach my thumbs down to my trackpad (which I actually do quite a bit when I'm on a roll). Using the Metro interface for app switching and launching, I would be reaching to my screen... and quite apart from the fact that I would end up with fingerprints on my screen (which annoys the hell out of me) I have just tried reaching out to the screen itself and found it intensely uncomfortable. I have to rotate my shoulders forward in order to reach it at all, my arms are extended at an uncomfortable angle. I would have to lean forward in order to use this comfortably and then my arms are no longer in the optimal position to type. This results in a lot of movement rocking back and forth, which while it may help me with my core abdominal strength a little does little for my back and is rather annoying. I have a good quality chair so I can sit at a decent angle for some time while working, without having to constantly shift around.
Sorry... I have used a Surface and it only works better than a laptop as a tablet... which the iPad also does just as well. I also run Windows 8 on this exact laptop I'm typing on, but after trying to live with Metro for two weeks I finally downloaded Classic Shell and find the entire OS transformed into exactly what Windows 8 should have been in the first place. There are a lot of other things I don't like, and Metro is the easiest one to fix... but yes it is the most visible problem with Windows 8. Of course, if Windows 8 had looked like my current desktop then Microsoft could never have sold it; it's far too much like Windows 7.