I downloaded the Windows 8 Consumer preview yesterday, and have it installed on a VM.
First, it seems to run very smoothly, even in a VM with only 2GB of RAM allocated. The problem with it is that A. there are a lot of unintuitive factors with it (like shutting it down, going to different menus, etc.) and using it with a keyboard and mouse is an enormous UI failure.
However, being so frustrated with it on a desktop, I kept thinking "wow, this actually will be pretty nice on a tablet".
Really, I think MS is making an enormous mistake if they plan to carry this through as a universal OS for both tablet and desktop/laptop. They really should separate the two.
As it stands now, I find myself really wanting to try a Windows 8 tablet, but am terrified of having to support this for users of desktops and laptops.
Windows 8 Server, on the other hand, is looking pretty damn cool.
The best things that they can do IMO is get rid of the incremental versioning (Home, Pro, Ultimate, etc), make one desktop version of Windows 8 loaded with features for the "power user" like a powerful BASH style console, etc, and turn the Windows App Store into a more powerful package management system and keep it open (like the ability to add new software sources). Windows 8 could be pretty sweet if they really market it towards the nerds, and Windows 8 Tablet Edition could be for the everyday tablet wielding consumer...because that seems to be the way things are changing.
With a bit of inspiration from the GNU/Linux world and some interface improvements Microsoft could have a winner, but Windows 8 is not looking good to me.