Change type signature of objectForKey: ?

[Richard Frith-Macdonald]

The -objectForKey: and -setobject:forKey: methods exist in  
NSUserDefaults and NSDictionary with two different type signatures.

For NSDictionary the key is of type 'id' but for NSUserDefaults it is  
of type 'NSString*'

This can cause a lot of irritating compiler warnings when using these  
methods, so I was wondering if we should standardise on the 'id'  
type, and just have NSUserDefaults perform a runtime check (or even  
use [key description] to be sure that a key is a string).
That would mean that the formally declared API for NSUserDefaults  
would differ slightly from the MacOS-X version, but it should not  
cause any problems that I can see.
What do people think?