What is wrong with using an NSObject hash to create an NSMutableDictionary key?

In several places, I need object mappings to objects and used NSMutableDictionary as a lookup table. The key was placed in the hash code of NSObject, for example:

  [dict setObject:newObject forKey:[NSNumber numberWithUnsignedInt:[keyObject hash]]];

where keyObject is an instance of a user class that inherits the implementation of the hash function NSObject - (NSUInteger) as-is. I saved the keyObject references elsewhere, which I can use to get newObject:

[dict objectForKey:[NSNumber numberWithUnsignedInt:[keyObject hash]]]

This seems to work so far, although the corresponding application is still young.

Matt Gallagher, however, writes about this approach:

(don't laugh, I saw it)

which undermines my confidence a bit (and since this is for an iOS application, I cannot use it suggested by NSMapTable).

- , NSObject , iOS?