I tried to give the new parts of Windows 8 a fair shot when I upgraded. I downloaded some new Windows Store apps, and I even left the Start screen intact and didn't install something like Start8. The result was an exercise in futility. I could only use one Metro app at a time on a 22" monitor, which was a horrendous experience. I could snap a window to the right third of my screen, but that would actually shrink the workable size of my desktop, and I couldn't find a single Metro app that was worth losing that much of my display real estate. This perfectly demonstrated the fundamental problem of trying to use Windows 8 on full-sized PC: all of the new features fight with the old ones in a very fundamental way.
To add insult to injury, I discovered that a new process in Windows 8 called Runtime Broker, which manages permissions for Metro apps, had run out of control. If a developer uses a certain API call to refresh a live tile too often, the amount of RAM the process uses balloons from about 2MB to 1GB or more. My machine was running poorly due to a Metro app that I had stopped using weeks ago and completely forgotten about. I finally ended up uninstalling every Metro app just to be sure the problem went away, so now I'm no better off than I was on Windows 7. Just minus a Start button.
I don't think my specific experience is typical, but I think the overall conclusion I came to is: I just don't see why Windows 8 is worth the money or time investment. I like the idea of a ubiquitous OS and interface and I want Microsoft to fully realize the goal its going for. But right now, Windows 8 doesn't offer any tangible benefits to its core userbase of desktop and laptop users, which is exactly the wrong approach a software maker should take.