If you over-do it then NSNotifications easily can become distributed goto. Once I had to add features to a Mac application that made heavy (ab)use of NSNotifications. Following code paths was a nightmare.
I tend to prefer the delegate pattern because there the relationships between objects are clear. Even if it means more work (creating glue code) - your sanity is worth it.
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A little off topic:
If you over-do it then NSNotifications easily can become distributed goto. Once I had to add features to a Mac application that made heavy (ab)use of NSNotifications. Following code paths was a nightmare.
I tend to prefer the delegate pattern because there the relationships between objects are clear. Even if it means more work (creating glue code) - your sanity is worth it.