Re: 2 camps
My productivity dropped when I tried to do my normal work on it. What more do I need? Fancy anecdotes? Factual benchmarks? Finding some reason for it? No. It dropped, and I couldn't get it back to XP-levels even with a hell of a lot of messing about.
Hell, compared to a properly organised XP "classic" menu, it takes me twice as long to find a program using the silly narrow-down search when I have hardly any programs installed at all. I need to get to dialogs inside control panel and other weird places and get there a lot on a lot of machines that may be configured differently and get there every time, consistently. I can't. Same reasons I rejected "Unity" or whatever it's called on Ubuntu. That, similarly, saw a single test and then went into the bin. Ironically, I now use Ubuntu LTS for server text-mode-only installs and Slackware for desktop installs.
I don't use the Metro interface. At all. I spent more time trying to get rid of it than I did using it (and you can't get rid of it permanently, which is literally a one-line code enforcement at MS for no sensible reason). Just because others might find it useful, I just find it getting in my way and making even more things take even more clicks to do than before (and I even tried it on a touchscreen!). Guess what? People work differently. You might love Metro, to me it's an extension of everything I hate about modern "desktops". I'd rather have an ugly, blocky, square, bland interface than all that junk. Hence why people call it "Fisher Price", etc. Yeah, looks really pretty. But I can't get used to using it and never have since XP.
Windows 8 boots fast and shuts down fast, that's about it. Everything else is just natural evolution (e.g. driver support built-in for more things, new types of technology support, etc.) and is pretty much Windows 7. The number of boots/shutdowns I do is absolutely minimal since standby became a stable solution in XP, so even the boot times mean NOTHING any more (and if I was that worried, I'd use an SSD).
Productivity costs. I don't *want* to train on an interface. I want it to work. When I do train on an interface, I expect to see the gains in productivity. I haven't, since XP. In fact, since then every Office and Windows has made me less productive. Ribbon toolbar and contextual junk is NOT FOR ME. I can't stand it. I want to turn it off. I hate suggestions that LibreOffice might try to go that way in the future. It's stupid and ridiculous and kills my productivity with unpredictability. But MS can't be bothered to give me an option and tell me I "must" do it this way.
These interfaces GET IN MY WAY. They STOP ME INTERFACING in certain ways. They MAKE INTERFACING DIFFICULT. No amount of training provides consistency in some parts of the interface (i.e. the narrow-down search changes depending on what you have installed!). Dialogs that I've been able to get to in two-three clicks for years (and not got in anyone's else's way) I now have to know magic incantations for, or go around the houses in non-obvious ways to get to the same point.
I can't remember what I was doing but it was something quite trivial like checking an IP address, finding a MAC address and then changing it to a static IP to do something. It took me longer to figure out than imaging the machine had. And it was such a convoluted way around because MS just wanted to hide that information and options from the administrator user. Hell, I know you don't tinker with that every day, but when you do it's nice to be able to find it.
Technically, Windows XP through to 8 have been good. They run pretty much the same programs, work on lots of hardware, each has their niggles but they get the job done technically. Usability-wise, they get worse and worse (and now Ubuntu is following suit). If you cater to the dumb user, you'll only get dumb users. Dumb users rarely make the call on what gets installed across sites or in companies of hundreds of employees, because they DON'T have to manage the machines and do the things that technical people do.
Honestly, from a personal perspective, I still use XP for purely usability reasons. If I'm "forced" onto other OS in the future, I'll just go Linux, because I *can* configure it how I like, use what start menu I like, use what desktop environment I like, and use an Office suite that doesn't force me to use ribbons and other rubbish (even if I have to stick with an old version of it). It's literally that important that I be able to get to options, right-click menus (which seem to have disappeared in Ubuntu's new interface, for example), technical details, etc. that I will sacrifice Windows compatibility for it. Work is a different matter but the same things will affect the same decisions.
Now, I work in schools, so also a problem is "small children". Get your child to run a program that's not on the desktop. Hope they can read and type the full, correct spelling of the program because otherwise you'll have to clutter their desktop with EVERYTHING they want to use! Get them to all write a letter as a group. They will ALL end up with different menu options in Office depending what stage they get to. It's not ideal.
Seriously - turn off the "#ifdef METRO, splat_metro_screen_over_desktop", re-enable the old Start Menu for those who want it, and get rid of any transparency, side-bar (god, that's annoying, especially when you hover near the right on a touchscreen), and all the other crap.
My desktop and start menu are my program launch interface. This destroys them. The other junk just pops things up unnecessarily all the time and gets in my way (hell, I had to answer a question about which browser I want to use on first logon now, as if it wasn't obnoxious enough when they pushed that through Windows Update). Gimme a desktop that's "dumb" and inactive. It shows me program icons, runs those programs when I click them and gets the HELL OUT OF MY WAY so I can use what I bought the machines for - running programs. Every time you hide something away, you are getting in my way. Every time you don't show full options, you are getting in my way. Every time there's ANOTHER step in the way I do things, you are getting in my way.
Seriously, the first person to bring up a minimalist interface on something that can run Windows apps will be a billionaire. I want to choose what happens on my own desktop (i.e. NOTHING should pop up and steal keyboard focus EVER). Apparently, that's not allowed. And, until it is, I won't be using it.