I'm not among the defenders of the postmodernist troika of Lacan, Foucault, and Derrida, but in the spirit of Daniel Dennett's line, "There's nothing I like less than bad arguments for a view I hold dear," I'd like to propose a moratorium on the extremely weak 'argument' that tries to criticize postmodernism by quoting examples of pomo jargon. Anyone who has read any of the anti-pomo literature has encountered many examples of this: polemicists who quote passages out of context from Jameson or Zizek or Hartman in order to argue that pomo is impenetrable, elitist, anti-American, and probably leads to gum disease. The most common counterargument--and I think it's good enough--is that since Lacanian psychoanalysis, Foucaultian sociology and Derridean linguistics are highly specialized fields, they have developed a highly specialized jargon comparable to that of other specialized fields. All specialists, from auto mechanics to cardiologists, from carpenters to concert pianists, speak a language that is at times impenetrable to the uninitiated. They use words like 'differential,' 'manifold,' 'aneurysm,' 'endovascular,' 'skirting,' 'architrave,' 'demisemiquaver,' 'ostinato,' and they use these words for the same reason pomo theorists say things like 'interpellation,' 'deconstruction,' 'subjection,' 'abjection,' 'aporia,' and 'zeugma': the specialized language is a rhetorical shorthand that allows them to talk more economically among themselves. Like any foreign language, postmodernist jargon ceases to seem impenetrable once you've taken the time to learn it. (Whether or not it's worth the time is a question for another day.)
On a related note, a reader on another thread has challenged me to explain Derrida in plain language. Here's my attempt:
Derrida begins with the idea that Western intellectual discourse--philosophy, linguistics, anthropology, literature, etc.-- has historically valued speech over writing due to the perception that speech, issuing directly from the speaker's mouth, has more presence, and thus more authority, than a written text. He then argues that this quality of presence in speech is an illusion because all language, spoken and written, is devoid of presence. This lack of presence is a fundamental feature of language because, as Derrida argues, language is a closed system that can refer only to itself. Words refer not to things in the world but to other words (definitions), each of which refers to still other words, ad infinitum. Language is free play, a dance over an abyss of meaninglessness. Any attempt to enclose language in meaning is a form of linguistic violence, an arbitrary exercise of power. One response to this hidden rhetorical violence is to reveal it through 'deconstruction,' a process that generalizes Derrida's initial approach to the speech vs. writing conflict and applies analogous techniques to the other seemingly stubborn dualities that define our lives: male/female, gay/straight, liberal/conservative, foreign/domestic, etc., etc.. The first step in the deconstructive process is to reverse the traditional polarity (the privileging of male over female, for example); the next step is to show that this reversal is equally illusory because it remains trapped in some arbitrary, historically contingent pattern of thought (in the male/female example, this would be the idea of strict, dualistic gender definitions); step three would reveal the hidden hand of patriarchal power in the definition of the idea of gender, thus dissolving the initial duality into a power-motivated rhetorical construction, a function of language.
This is grotesquely simplified and doesn't even attempt to glance at all of Derrida's writings, but I think it's a fairly clear and reasonable nutshell of the most influential part of his thought and its political utility.