Gave it a spin in a VirtualBox VM today. Seems OK I guess, not much point echoing the facts people have already mentioned, performance etc.
The spilt windows thing is OK, still nobody has resolutions wide enough to make use of it unless you use >1920x1200. I use a portrait display anyway so that was useless to me. Dragging the window to the top of the screen to maximise? WTF, there's a button for that, there always has been. They do add some pointless features.
I quite like the taskbar, no need to have the program names there once you know what the icons mean. A bit like the OS X dock I guess.
Action center and control panel seem a little better than Vista, although I see 'set up a wireless device' way too many times.
...And then there's IE8. Haven't used this before due to it being beta etc. Fire it up, first site I go to is the latest web application I'm working on. Positioning is out. Thank you m$, so that'll be ANOTHER conditional stylesheet then