HTML5 Canvas Performance - should we be worried?

Here is a Tweet from Grant Skinner that surprised me, since Grant is one of the pioneers in Canvas development, having his team develop EaselJS, a framework that puts sense into the mess we call Canvas.
Grant claims that HTML5 Canvas performance is something to be worried about, as it appears to be sluggish, and I must say that from the experiments I've done with it, I've noticed that too...
Knowing Grant's work, I'm pretty sure that he had tested and benchmarked all there is (and probably still is) to back his assessment.

I, like Grant, would really like to know what Steve Jobs has to say about it.