[rimantas]

  > "native performances" still makes sense if you are talking 
  > about building physics engines or whatever kind of heavy
  > simulations, but not for 90% percent of the smartphone
  > apps today.

You have no idea what does it cost to have 60fps scrolling of the non-trival view.

Update: after watching this video: http://www.youtube.com/watch?v=Iu8q-oISbas I do not understand how anyone can call UI responsive and maintain a straight face. Or I do not know what are you comparing it to. Just take a look how the contacts app works :(

[nical]

I do have ideas. I also have a decent knowledge about how Gecko's graphics engine works internally. And again, the expensive operations (actual image rendering, layout computation, compositing, etc.) all happen in the platform, that is in "native" C++ code. What it costs to to have a good scrolling experience is to write your app in a way that doesn't cause the engine to over-invalidate and compute reflows all the time. Or it costs beefier hardware, but then this is not part of the debate of web vs native.