The official Twitter app for Android was updated to version 2.0. In this version Twitter seems to move away from the original design that was created by Google as a reference implementation of the Dashboard and Action Bar design pattern. This Twitter app no longer has the Dashboard but launches to tweet list directly.
In my opinion this is a justified move as Twitter's simple functionality doesn't really present any difficulties to users. The application functionality is clear and easy to understand and reading tweets is probably the most used use case of the app.
They still use the Action Bar design pattern.