Even though I’m an existing user of Twitter for iPhone, I found the intro screens for its newest update to be an interesting form of a first time user experience. Information panels overlap the lower portion of new content screens and you swipe through them to get a sense of the app’s new structure. What is most interesting about these is that they maintain your Twitter content in the background, as it would normally appear, so there is a familiar context as you go along.
Something I’d suggest Twitter look at, however, is to let someone exit the intro mode without having to swipe to the last tab. Because you have contextual info in the background, folks may be more inclined to start interacting with it, and may expect tapping outside the intro panel to collapse it.