After a week of trying to push Sencha Touch to do some very simple UI tasks, I have to conclude that it just is not ready for playing, let alone production work.
The worst part of Sencha is that the API documentation overlaps with ExtJS so much, yet is different enough that sample code for ExtJS doesn't just work. So the normal trial and error of using forums and blog postings to supplement docs is made that much more ineffective.
I'd like to say Sencha Touch shows promise, but I can't.
It isn't just the grinding I've done finding so much conflicting info and dead-end paths.
It isn't just the incomplete, apparently untested code that belches "undefined" error messages for documented methods and properties .
The API just doesn't make simple things simple and difficult things straightforward.
At least for now it does not appear that there are clear idioms guiding how various hooks and extensions are accomplished. Maybe after the dust settles from the on-going development it will be a consistent and clear API. But for the moment, as of September 2010, Sencha Touch is more of an interesting experiment - or an annoying one, depending upon how much you took for granted the stability and soundness of the code.