In a Flex app, I like to have the StateMachine utility control my application states and have mediators in charge of hearing about those changes and coordinating the appropriate view states. It's nice to have states in Flex, but not necessary. You can encapsulate the states of your views in your view component classes and expose methods that mediators use to trigger view state changes, and events you dispatch that tell your mediators about the view state transitions completing and the like.
There is a short introduction to the utility at
http://puremvc.tvCheers,
-=Cliff>