Only those objects that will never be source objects in relationships with unshared destination objects can be shared. Shared objects should be read-mostly as well because updating them requires a special procedure.
\[I personally have always been scared of using EOSharedEditingContexts, because there seemed such potential for problems. They are complex in how they work, not entirely well documented, and I suspected there would be Apple bugs. Wiki Markup
Robert A Decker
However, one user kindly provided his own guidelines he uses with EOSharedEditingContexts, and which he says results in no problems at all. I include his guidelines here.