They are very smooth for me. I suppose because I have good GPU and IE9 likes my GPU. It is quite awesome actually. I wonder what this means. Should be really drop everything and use HTML5? If MS is able to make a layer that can runs WPF/XAML and XNA on HTML5, that would be very interesting.
Remember to change to IE9 Doc Mode, the site set it to IE8 Document Mode, arrrggg.