Cubism predates postmodernism by at least thirty years,
and probably by fifty or sixty, depending on when one says postmodernism began. So the only way it could be, as bunkey writes, "the epitome of (...) what is wrong with postmodernism" is for what is wrong with postmodernism to be that it just happens it isn't as old as cubism. But enough about that.
A cubist piece of art to me seems to be an abstract explosion of the subject, so that every
single line of the original is visible. I'm not
sure if I'd be willing to equate this sort of
decomposition and recomposition with deconstruction.
Two artists influenced in different ways by cubism
were Piet Mondrian and Gertrude Stein.
A short article on cubism is available online at http://metalab.unc.edu/wm/paint/glo/cubism/ .