It depends very much on the browser. Ironically, IE is leading in that area, actually, and Firefox lags behind the other two by a great margin. It often looks like FF thinks it needs a complete repaint where a little recompositing would suffice which means that something as simple as moving a tiny thing in a large, complex visualization can have abysmal performance.

It also seems that, depending on the browser, they have dug themselves in the same hole as before. Moving the polygon or one of its nodes around triggers a layout in at least Chrome and IE, exactly what they wrote were trying to get rid of. Maybe the demo does not yet show their new implementation; I saw way too many SVG elements, but no CSS transform on them.