I had the opportunity to play around with a Yoga Ultrabook and Vivo RT tablet yesterday...
All I have to say is Windows 8 on a touchscreen is damn impressive. I spent the most time with the Vivo tablet and Windows 8 RT is super smooth It's fast, fluid, responsive, no lag whatsoever. It was exciting because the Vivo is so close to the Surface I preordered in terms of specs. I got some pictures and a video of the two as well. The screen is comparable to my iPad (3rd Generation) and may even have better color reproduction (in my opinion (don't flame me please)). Overall I'm more than excited!