I'm a tad confused about the turn based option with iOS5. Does this take care of everything needed to make a multiplayer turn based game?i.e all the game turn data is stored with apple or do I need to still provide a server for something?
You don't have to provide any server when using game center, if the player are close enough they can connect via bluetooth if not than they will be connected via internet through apples server for game center.
The only thing you need to do is to import the GameKit framework in your class and use appropriate methods to handle the events in your turn based game.
Also here are the links of the classes that you might use of game kit framework.
and here are some examples that will provide a good explanation for the game event handling.