[egfx]

I have used Breeze and it works beautifully. It is a bit complex but the results give you a very native like experience.

Ward Bell talks about it briefly here: http://www.viddler.com/v/94a02c0f

There are a few google talks about it on youtube too if you look. It's great for enterprise.

[pc86]

The fact that you even have to use phrases like "a very native like experience" should be enough to show you that JS+HTML5 is not yet enough.