All of my previous comments have been around using ExtJS and not SenchaTouch so today, for the first time, I'm building an ST app. I'm not sure how important this is but I thought I'd give my initial feedback and points where I could have given up (but of course did not)
I first started by dropping a toolbar on the design surface and adding some buttons. It showed correctly on the design surface but did not work.
Then, I thought I should put a top level container around it. So, I added the top level container, dragged my toolbar into it and that still did not work (though looks correct in the designer)
Finally, I marked the container as my initial view and then finally it worked.
Since in the first 2 cases I did not get any errors or warnings I noticed, I think that scenario could be improved. I'm not sure if you've gotten this feedback, but I think first impressions are 10x more important than impressions after the fact.