I get the following error in my console:
Applications are expected to have a root view controller at the end of application launch
I got this when starting with the "Empty Application" template and then manually adding a XIB. I solved it by setting the main Nib name as suggested by Sunny. The missing step in this scenario is removing
self.window = [[[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]] autorelease];
from
application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
As it will overwrite the instance of your window created in the Xib file. This is assuming you have created a ViewController and wired it up with your window and App Delegate in the XIB file as well.