I've been running 8.1 for a couple of weeks. It is just a games machine, but I have some observations:
1. Things move. It isn't just different, its inconsistent. If I want to power off/sleep from the desktop I have to go bottom left, click on windows start-screen button. Then I have to move to the opposite corner (top right) for the power icon, then scroll down for the option I want. There's far to much movement.
Worse, sometime I've noticed that the power button comes up on the bottom right bleed-in panel.
2. pin to taskbar / icon on the desktop is a workaround for the start screen. I use this a lot. I did on Win7 too.
3. Start screen is full of MS rubbish. You have to delete all the MS junk from the start screen one at a time (no multi-select of icons appears to be available): select an icon, from somewhere on the screen, then click on the delete menu which just appeared (so you couldn't see where it was earlier and plan your mouse moves) at the bottom of the screen which is far too much mousing. There isn't even a rubbish bin shown to drop stuff straight into.
Then you have to replace the icons with useful stuff - control panel, explorer, Firefox :) and your other real apps. I shouldn't have to clean my environment on a fresh install - that just looks bad like pre-installed OEM crud. It's also tedious to remove and oh how I hate live tiles. It's like looking at a facebook page.
4. PC Settings. You'd think this might be the control panel. It isn't, it isn't that useful and it doesn't appear to have a link to the control panel. Where are my £$%^&* network settings? PC Settings is at the bottom on a right-side auto-hide panel along with some other stuff.
5. Menus/results. Right-side panel (lower) for some things, left side "start button (lower) on the desktop, almost top right for the start screen menu and search results. The menu's are all over the place with no apparent reasoning.
6. Going along with the theme. Click the start screen button (bottom left) and your apps appear not in the bottom left where your mouse is, but all over the screen - again far to much mousing. If I have a lot of apps and start typing in the application name, my filtered list appears in the opposite corner to where my mouse was. Yes I could use keyboard shortcuts but it's supposed to be a WIMP environment.
Or rather it isn't. This is a touchscreen, not mouse environment. Things are organised for fingers on opposite hands to be used in a coordinated fashion on a tablet-sized screen. It's rubbish for mouse-based operation on a 27' monitor.
Here's the difference between how Apple introduced IOS and how MS introduced Win8. With Apple, I was never left thinking "I don't know how to do X." Perhaps because it is an inherently simpler environment. With Win8 I'm constantly having to think how to get past the GUI to my applications or data.
Maybe its just my personality but I like structure, organisation and predictability. Search is a last resort when I've forgotten everything else or misplaced it. I don't want to be forced to search visually through a large screen of icons and neither do I want progressive search with its shifting icons and dynamic lists to be my main mode of access. Win7 search was fine, KDE search is fine, both attached to the start menu (and alt-F2 for kde). It feels like a desperate attempt to make windows cool by making it look as though "Windows just knows where everything is" rather than "I installed my app in that location and stored my data in that location."
MS needs to get over itself and concentrate on what it knows. By the time it's ready for mobile, mobile will be saturated and the market gone. Get some better local caching in Outlook so my laptop talking to the corporate mail server on the other side of the world doesn't spend ages trying to update its social media integration data. That would be nice.