Thanks, Robert, for starting this topic. Even before I saw Jorge's first response, Serrano's "Christ in Piss" came to mind. As a believing Catholic, I found Serrano's work to be extremely offensive. But, except for it's shock value, his work is throughly mediocre, and therefore, transitory,as well.
I, respectfully, disagree with Ed, about the subjective relativism of art. Art like Philosophy, Theology or Literature often (mostly) responds to events, i.e., is topical. As an example, Philosophy, after the Renaissance, increasingly became concerned with examinations of Scientific Method and Phenomenology, to the point, in the early 20th century, Philosophy was mostly about epistemology. Socrates question, What is the good?" was just as relevant, it just wasn't being asked. Metaphysics, queries concerning the transcendent, eternally part of Philosophy were being ignored. Most of art, too, responds its time and circumstances. Most of it is transitory, but the great non-subjective work is not. Think Pieta, Stary Nights, Mona Lisa, Cantebury Tales, and maybe, Clearing Winter Storm.
Great art, though created in time, is that which outlasts the subjective and temporal evaluation. Serrano's "work", whatever the immediate impact, will be forgotten very quickly.