I'm using it as my main OS on the desktop. I haven't installed it on my HTPC or laptop though.
I have gotten used to the smart screen. Learning the Win+I shortcut was huge, as was realizing that apps can place things in the settings menu.
The main reason I haven't put it on all of my machines is that it feels like a beta. My wife wouldn't be happy with a beta OS on the HTPC. I'm hoping for a public RC so I can take it for another spin. After some initial disappointment, I've gotten used to it and don't really have a problem with removing the start menu. The mouse gestures work fine for me, and my next computer purchase will probably be a tablet, so it will be nice to have the same OS on everything.
Am I writing Metro apps? Nope. I don't think we'll see a large move to WinRT for at least a year after Win 8's release. There just won't be enough of an installed base, unless the OEMs have some nice inexpensive tablets in the wings.