I recently developed a simple login module using Echo2 and it was mind boggling with the ease of use it provided to me.
In first place the problems it solved was the back button problem as only a single page is being used to render the views. The view changes on a successful login else it keeps showing the same page with a error message at top of the page.
Only pain point is the binding of data but I see things emerging with api's like bean view helping the cause. But this is a major step in bringing desktop look and feel to the web. It seems like a VB application on a web page.
Another fwk in the same domain in zk .It gives some cool UI but I didnt explore much of it.