This might be a straight forward answer, and I know that you don't have to set NSObject as the Superclass when creating a new class.
But say, for example, I wanted to create a class which held a set of custom CABasicAnimations. Although it may be perfectly ok for me to use CABasicAnimation as the superclass, is it recommended that I follow the unwritten rule and still use NSObject or would you, if you were writing such a class, use CABasicAnimation as the Superclass?
I would assume that it wouldn't matter as long as the Class only contained properties and methods relative to CABasicAnimation.
It would be interesting to here your thoughts!
The rule is to subclass whatever object you are trying to extend. NSObject is used for many subclasses because it is the root object, but if I was going to write a class that was very similar to NSTableView, then I would subclass NSTableView.
In your case, if you are writing a custom animation that you want to call, then you should consider subclassing from CABasicAnimation. On the other hand, if you animation is really just a collection of pre-exisiting CA animations, then NSObject would be fine.