Using NSUserDefaults is great when you want to save small amounts of application data such as log in, last settings, etc
An Example
Saving
NSUserDefaults *NonVolatile = [NSUserDefaults standardUserDefaults];
[NonVolatile setObject:@"TextToSave" forKey:@"keyToLookupString"]; //Saving an NSString
[NonVolatile setInteger:42 forKey:@"integerKey"]; //Saving an NSInteger
[NonVolatile setBool:YES forKey:@"boolKey"]; //Saving a BOOL
[NonVolatile setDouble:3.1415 forKey:@"doubleKey"]; //saving a Double
[NonVolatile setFloat:1.2345678 forKey:@"floatKey"]; //Saving a Float
[NonVolatile synchronize];
Reading
NSUserDefaults *NonVolatile = [NSUserDefaults standardUserDefaults];
NSString *myString = [NonVolatile stringForKey:@"keyToLookupString"]; //Getting an NSString
NSInteger myInt = [NonVolatile integerForKey:@"integerKey"]; //Getting an NSInteger (default if not present: 0)
bool myBool = [NonVolatile integerForKey:@"boolKey"]; //Getting a BOOL (default if not present: NO)
float myFloat = [NonVolatile floatForKey:@"floatKey"]; //Getting an Float (default if not present: 0)