ObjC’s concept of categories has some problems when you use it too much – name conflicts!

Best practice is to prefix your own private categories (as there are no name spaces).

And you should really do that – some iPhone Apps are rejected currently for using categories that override default code.

Set the environment variable OBJC_PRINT_REPLACED_METHODS to YES to see warnings when such name conflict happens.

Update: (comment from DaringFireball)

Overriding private methods in a category is far worse than calling them directly.

Everything in your process will get the overridden behavior of the private method and assumptions about side effects go out the window.

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