I switched to Backbone and got going right away, in half a day of reading the docs and watching a couple of peepcode videos and I was off and didn't look back.
Maybe the Ember docs have improved in the last couple of months but at the time it was just a non-starter for me.
edit: I believe the issue was around Ember Data/REST. Out of the box it didn't support polling data on a REST interface, which seemed absolutely critical/fundamental to a JS framework. I found a plugin I believe called Ember Data, but documentation was very sparse and I couldn't even get a simple example going. This is going on memory so this could be slightly wrong or different today.