I downloaded the $40 upgrade last night and installed it over an existing Win 7 installation.
I've used a Windows 7 phone since they first came out, so the user interface was not all that new to me, although I had some doubts about how well it would translate to a non mobile device.
In short, I really like it - it's even better on a desktop than on a mobile device. I'm actually a bit shocked at how similar it is to the mobile platform - go to the app store and download the app for what you want to do, pin it to the start screen, and that's that.
The bleating about not being able to access the desktop, I mean, really, JOD is right on this ... just how hard is to hit the tile and bring up the desktop?
And why would you even want to? If it's something you use, just go to all apps and pin it to the start screen.
Will I upgrade my business computers to it? Haven't decided yet. They're a mix of XP and Vista and work fine at present. Not sure it's wise to fix something that not's broken when $$$ are involved. But for a phone, tablet, home computer, I think it's just great.
I see a change from my Windows 7.5 phone to a Windows 8 phone in the next week or so.
edit: As an aside, I was at Best Buy yesterday with the intention of buying my wife a new iPad to replace the original iPad I she has. But after playing with the Surface, and then looking at the new iPads, the iPad just totally blows. I can't imagine anyone wanting that tacky, static, user interface vice the dynamic and customizable Windows 8 interface. If she wants a new fruit toy, the cost is going to be on her. I'll buy her a Surface, but not another fruit pad or fruit phone.