I am of two minds about this. On the one hand, he's right. I shouldn't return stringified results for objects/references. On the other hand, comparing object id's is almost never what you want anyway when comparing objects because it just isn't that useful.
In the vast majority of cases when you're going to be working with sets of objects, you should subclass and define your own methods to work specifically with those objects. For example, if I have $f1 = Foo->new(1,2) and $f2 = Foo->new(1,2), then for all intents and purposes $f1 and $f2 are identical.
Of course, the real reason I'm arguing is that I'm feeling lazy and I don't want to have to go back and fix my module.