Did you find a suitable alternative to Ember?
I went with Amber in the end. I can't remember if it was more or less painful initially, but at that point I had spite in my fingers.
Not sure if there's also a lesson in that for startups: will you get lucky with some users just because they've had a bad experience immediately prior to checking you out?
I used it to build a very basic Jabber/XMPP client in a little over a day, integrating with an existing system.
That's the only project I've used it in so far, and I'm still very much a beginner user.
All I can say is that it solved a problem with the minimum of fuss and inside quite a strict time budget, so I'm very happy with it.
Plenty of very good introduction videos on youtube