Good to see you back, Shona.

Of course, as far as I am aware, it was this paradox (or one akin to it: "The set of all sets that are not members of themselves") that caused Russell and Whitehead to give up on their Principia. Also was probably what set Godel off on his Incompleteness Theorem - one of the most important epistemological results of this century (probably equal first with Heisenberg and Uncertainty). So all hail the humble paradox!