app.rb

app = UIApplication.sharedApplication

NSLog "statusBarHidden #{app.statusBarHidden.inspect rescue nil}" # fails (documented)
NSLog "statusBarHidden? #{app.statusBarHidden?.inspect rescue nil}" # passes (undocumented)
NSLog "idleTimerDisabled #{app.idleTimerDisabled.inspect rescue nil}" # fails (documented)
NSLog "idleTimerDisabled? #{app.idleTimerDisabled?.inspect rescue nil}" # passes (undocumented)
NSLog "networkActivityIndicatorVisible #{app.networkActivityIndicatorVisible.inspect rescue nil}" # fails (documented)
NSLog "networkActivityIndicatorVisible? #{app.networkActivityIndicatorVisible?.inspect rescue nil}" # passes (undocumented)

### However:

NSLog "applicationSupportsShakeToEdit #{app.applicationSupportsShakeToEdit.inspect rescue nil}" # passes (documented)
NSLog "applicationSupportsShakeToEdit? #{app.applicationSupportsShakeToEdit?.inspect rescue nil}" # fails (undocumented)

### Also a small inconstancy when running from RM console:

(main)> app = UIApplication.sharedApplication
=> #<UIApplication:0x9315b90>
(main)> app.statusBarHidden?
=> 0 # <-- Displays 0 or 1 instead of true or false

app_delegate.rb

class AppDelegate
  def application(application, didFinishLaunchingWithOptions:launchOptions)
    @window = UIWindow.alloc.initWithFrame(UIScreen.mainScreen.bounds)
    @window.rootViewController = HelloController.alloc.init
    @window.rootViewController.wantsFullScreenLayout = true
    @window.makeKeyAndVisible
    true
  end
end

hello_controller.rb

class HelloController < UIViewController
  def viewDidLoad
    self.view.backgroundColor = UIColor.whiteColor

    app = UIApplication.sharedApplication

    # Documented statusBarHidden causes NoMethodError exception:
    NSLog "statusBarHidden #{app.statusBarHidden.inspect}" 
    #
    # (main)> 2012-11-29 18:13:38.660 bug[4380:11303] hello_controller.rb:6:in `viewDidLoad': undefined method `statusBarHidden' for #<UIApplication:0x9454ee0> (NoMethodError)
    #   from app_delegate.rb:6:in `application:didFinishLaunchingWithOptions:'
    # 2012-11-29 18:13:38.662 bug[4380:11303] *** Terminating app due to uncaught exception 'NoMethodError', reason: 'hello_controller.rb:6:in `viewDidLoad': undefined method `statusBarHidden' for #<UIApplication:0x9454ee0> (NoMethodError)
    #   from app_delegate.rb:6:in `application:didFinishLaunchingWithOptions:'
    #

    # Undocumented statusBarHidden? works fine,
    NSLog "statusBarHidden? #{app.statusBarHidden?.inspect}"

    # Documented idleTimerDisabled causes NoMethodError exception:
    NSLog "idleTimerDisabled #{app.idleTimerDisabled.inspect}"
    #
    # 2012-11-29 18:18:35.909 bug[4521:11303] hello_controller.rb:20:in `viewDidLoad': undefined method `idleTimerDisabled' for #<UIApplication:0x76237f0> (NoMethodError)
    #   from app_delegate.rb:6:in `application:didFinishLaunchingWithOptions:'
    # 2012-11-29 18:18:35.911 bug[4521:11303] *** Terminating app due to uncaught exception 'NoMethodError', reason: 'hello_controller.rb:20:in `viewDidLoad': undefined method `idleTimerDisabled' for #<UIApplication:0x76237f0> (NoMethodError)
    #   from app_delegate.rb:6:in `application:didFinishLaunchingWithOptions:'
    #	

    # Undocumented idleTimerDisabled? works fine.
    NSLog "idleTimerDisabled? #{app.idleTimerDisabled?.inspect}"

    # Same story with networkActivityIndicatorVisible vs. networkActivityIndicatorVisible?
    NSLog "networkActivityIndicatorVisible #{app.networkActivityIndicatorVisible.inspect}"    # Fails (documented).
    NSLog "networkActivityIndicatorVisible? #{app.networkActivityIndicatorVisible?.inspect}"  # Passes (undocumented)
    
    ### However:
    NSLog "applicationSupportsShakeToEdit #{app.applicationSupportsShakeToEdit.inspect}"      # Passes (documented).
    NSLog "applicationSupportsShakeToEdit? #{app.applicationSupportsShakeToEdit?.inspect}"    # Fails (undocumented)
  end
end