I'm particularly interested – if anyone has experience using Ember – about the concerns raised about Ember's performance with large amounts of data and "hairy custom view situations," as borismus puts it. Is Ember actually going to be slow when dealing with large data sets?
About 10 months ago, Strobe was trumpeting the "Ember" model for views (auto-updating templates, heavy nesting, bindings everywhere) and a lot of SproutCore developers began to use it.
The bloom is definitely off of that rose. At the latest user group meeting three weeks ago, many developers spoke up about having to remove all of their template view code because the performance was absolutely terrible.
At this point, "Ember-style" template views have been relegated to a separate opt-in library, are only being recommend for lightweight read-only data, and the recommendation for developers to use them is being removed from SproutCore's documentation.