A while ago I remember seeing a constant of some kind that defined the animation rate of the Keyboard on the iPhone and I can not for the life of me remember where I saw it.
UIKeyboardAnimationDurationUserInfoKey now is a NSNumber object, that makes the code shorter.
- (void)keyboardWillShowNotification:(NSNotification *)notification
{
NSDictionary *info = [notification userInfo];
NSNumber *number = [info objectForKey:UIKeyboardAnimationDurationUserInfoKey];
double duration = [number doubleValue];
}