Xcode 4.2 iOS Empty Application and storyboards

Comment out (or remove) the window creation and display code in AppDelegate.m as follows:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
    // self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
    // Override point for customization after application launch.
    // self.window.backgroundColor = [UIColor whiteColor];
    // [self.window makeKeyAndVisible];

    return YES;
}

When using a storyboard, a main UIWindow is created for you automatically. What is happening in your case is that you are creating another white window and putting it over the top of the tab UI.

ALSO – note that the Master/Detail template also gives you a core data option.