Ember.js is the new name of Sproutcore 2.0. I didn't know and it is very interesting because Sproutcore was the seed in my mind that helped me build Yoshioka. Here's the story.
Then, some months later, YUI3 published some MVC modules in experimental state. This modules was very easiest to use when you have habbit to work with YUI, so I started to work with it immediately. And then, I decided to apply all the great ideas I learn from Sproutcore into YUI3 MVC : live compilation, separation of template files, localizations, fixtures, etc.
The bad sides of this framework is the Cocoa approach and the very closed framework. It is very difficult not to walk into the path. That was the feeling I had 3 years ago and it was the same thing that told Raphaël Rougeron who was talking about Ember.js. With Yoshioka and YUI, you are free and invited to rewrite the wheel every time you need it. I love rewriting the wheel because the wheels never fit perfectly for what I want.
Another bad point is a memory leak. I used to have similar issues on Yoshioka with dynamical locales. Ember comes with a cool feature wich is able to update a variable into a template without full re-render it. It's the same behavior I chose for locales : an element (a span for Yoshioka) with an ID, and an observer which update the value of the node when the attribute of the model change. The problem is this node and observers are very difficult to clean and they are never free to be removed by garbage collector. With a workaround in the way Yoshioka locales are updated, I gain some hundred MBits of RAM. Overblog was able to occupy 600MB of RAM with a eavy use of the app. Now, it rarely jumps over 150MB. Raphaël talked about 2Go of memory on their apps.