My UIViewController class has an IBOutletCollection containing several IBOutlet objects. I am aware of the need to set retained outlets to nil in viewDidUnload, but do I also need to set the IBOutletCollection to nil? Or should it be released instead in dealloc? Or left alone altogether?
You need to set your outlets to nil in viewDidUnload in order to make sure that as much memory as possible can be released by the view controller when it receives a memory warning. In response to the memory warning, the view controller releases its view in order to free the memory the view (and all its subviews) is using. If you fail to release those outlets that you are retaining/holding a strong reference to, the subviews referenced by those outlets will not be destroyed and their memory won't be freed.
So yes, you should also set the property of an outlet collection to nil in viewDidUnload.
This requirement is independent of the responsibility to release all your retained ivars/properties in dealloc.