Completely frustrated as well
I am frustrated about the changes in Beta3 as well. Besides a lot of new bugs that have been introduced the API has completely changed, namespaces have been completely reshuffled and the examples are either minified or using black magic.
Up until Beta 2 I was very excited about the changes and the rate of bug fixes, but not so much now. In fact, I am thinking about dropping ExtJS 4 altogether until a final release is available. I spent a lot of time creating an application that worked on Beta 2 which now has to be completely rewritten. I understand that some changes still need to make it into the release, but changes like these, without any warning or description, is not very nice to the development community that is participating in testing the beta (?).