[lukeschlather]

>Most JS use is sparing and lightweight

Have you used Twitter or Facebook on resource constrained machines? Even on latest nightly builds of Chromium it's painful on my Dell Mini netbook.

The point is that you can use Javascript do just about everything you can do in Flash. And Adobe CS6 will almost certainly contain some tools to help you use your existing Flash assets in a pure JS+HTML+CSS environment. So the animation studio for Javascript doesn't exist yet, but we're talking about the near future where it will and it will be just as obnoxious as Flash (but much harder to block from consuming CPU.)

[spiralganglion]

The new Twitter really is the worst, and it's not just the Javascript. They've got that hovering topbar with an RGBA shadow and gradient background, which I've personally verified as being a source of much of the slowness on browsers that support these things. You can test it for yourself in any Webkit browser or FireBug — just disable those two CSS properties, and new Twitter feels immediately snappier.

Imagine what Gmail would be like if they went overboard with CSS.