Yes, there is. Usernames and Passwords should be saved using Apples Keychain.Keychain is encrypted by default. https://developer.apple.com/library/ios/documentation/Security/Conceptual/keychainServConcepts/iPhoneTasks/iPhoneTasks.html
Also, take a look at this tutorial on how to use Keychain in iOS. http://maniacdev.com/2011/07/tutorial-how-to-use-the-ios-keychain-to-store-names-and-passwords
To save other user preferences, use NSUserDefaults.