I've been using it...
...on my #2 machine and it's fine. The whole Metro thing is a bit of a nonsense but as a launcher it works okay. I have got rid of all of the "shortcuts" to the Metro apps and just have useful stuff on there - every one of which opens in the desktop environment. Other than that it is basically Windows 7 with a modded UI so if I was to buy a new machine with it pre-installed, I'd keep it. Can't see me rushing out to buy it though.
My only gripe? Having to log and then go to the log in screen to shut down - something I've noticed an increasing number of the Linux distros I've come across recently seem to have. My main work machine is a Mac and that very rarely gets shut down but at least I can shut it down without logging out first.
Overall? I'm pretty much entirely neutral about W8 although I don't approve of change for change sake. A new UI with more-or-less identical functionality is pointless and W8 strikes me as that, as do most recent releases of Office, OS X and that godawful GNOME 3.