> But have you tried doing anything graphically complex in HTML5? ... Things that Flash used to laugh at will bring Chrome to its knees.
Agree. An example is graph visualization. Fire up your CPU monitor and go to http://arborjs.org/atlas/ and view this very cool physics-driven mesh visualization written in Javascript. You'll see the needle jump to 95% or more. On my relatively modern laptop, if I run this for more than a few minutes, it shuts off due to overheating. Also, this app does not work on IE.
By contrast, I can run an similar Flash-based visualization and CPU usage ratchets up to 60 or 70% but not more, and it works on IE.