Sencha has the latest on the new iPad’s HTML5 performance, and the verdict looks quite good:
The iPad 2’s Mobile Safari browser is the best implementation of WebKit on a mobile device. In our testing we tried to throw everything we could at the browser and it had no issues keeping up with the most advanced HTML5 and CSS3 sites. For any developer building for the mobile web, the iPad 2 provides an outstanding platform from which you can use modern browser features.
It will be exciting to see how some of our newest Web-based software performs on this device, especially given these advances.