The Flickr iPhone app has a two-part approach to their first time user experience.
The first part of their approach goes against one of my primary principles for good first run design: let the user interact with content before asking them to create an account. When you ask for an account up front, you’re essentially putting up a giant wall.
The second part of the app’s approach is that it provides in-place hints. After you do sign in or register, you are brought to the home screen populated by people Flickr recommends following, and helpful hints then appear as you traverse certain areas of the app. While it is questionable whether some of these elements need explaining, they are limited in number and focused on those key elements that will add the most value to your experience.