Joanna Stern from This is My Next was able to get a demo of the quad-core NVIDIA Kal-El based Windows 8 tablet from VP of Windows planning Michael Angiulo at the BUILD conference. She posted:

We’ll admit, it wasn’t a very in-depth demo, but we were able to see snappy transitions between the Desktop and Metro interfaces. Even better, scrolling on the Start screen was nearly as smooth as that on the Samsung Core i5 developer tablet. You’ll see in the video below, he was able to swipe through open apps as well as open Windows Explorer.

The video below is the first and only live demo of Windows 8 running on an ARM based processor, NVIDIA Kal-El. And it clearly shows that the Metro UI is working smoothly on ARM.