For testing purposes, I've tried an upgrade from Windows 7 to Windows 8. It's simple and straight forward for the most part, but if you're someone who dual-/multi-boots then you might come across some quirky behavior.
Here's what I got when I tried it: Windows setup failed to detect if my PC is able to support Windows 8. Those aren't the words used but that's how I understood it. The problem? The first boot device set in BIOS wasn't the hard disk that contained Windows. Just swap things around in BIOS, boot into Windows and re-try the upgrade.
I got a similar problem earlier when I tried installing Windows 7 so it's something that's part of Microsoft's Windows setup.
Remember to write down that Product Key before you even start the installation. Here's the key:
And don't just copy and paste it somewhere. Write it down. Unless you're installing into a virtual machine, you won't be able to access it otherwise.
If you're upgrading, then you'll be able to migrate settings, apps, and personal files over. Just how thorough the user migration feature is, I have no idea. I tried just migrating personal files and didn't lose anything, if that helps.
The installation is pretty quick, and you get to do more customization after the reboot. It's the usual 2-step Windows setup.
Once you're in, you'll be experiencing something like what's in this recent video.
It's a horrifying experience. I'm no expert, but I consider myself tech savvy enough to at least be able to find my way around simple daily tasks (browsing the web, managing my files, etc...), and to figure out how to customize settings to my liking.
I hope either Firefox for Metro or Chrome for Metro will already be available by the time Windows 8 comes along because IE Metro is a terrible experience. If you thought the IE6 experience couldn't get any worse, you're wrong. It can and it has.
The only takeaway we have is that this is still a Consumer Preview although everybody seems convinced this is going to be the final UI experience we can expect. Let's hope the dissenting voices out there are enough to change things for the better.