The docs I've read seem to indicate the intended purpose of the tab bar at the bottom of an application window is to provide access to different modes; the Clock app is a good example of this. On the other hand, we have applications like Mail which seem to use the bottom bar for actions (like creating a new message). I have an app which would similarly benefit from using the tab bar at the bottom for actions, so I am wondering -- is this OK from the standpoint of the common user interface guidelines? Am I ruining some iPhone goodness if I design my app in this way?