You may agree, disagree or more often than not, just plain not understand Žižek and his extensive, frequently digressive commentary on the omnipresent, lurking-on-the-sidelines-but-not-quite-visible-yet-silenty-influencing/manipulating-everything-all-around nature of "ideology"; but it's hard to not find him immensely entertaining. His hyperactivish, super-heavy-East-European-accent-laden, verbally incontinent commentary makes for mostly incomprehensible but supremely engaging listening. Add to that his frequent examples/instantiations, drawn in a large part from popular and arthouse films, from Hitchcock and Wachowski Brothers' to Tarkovsky and Frankenheimer's; and the spell is complete - his filmic, discursive and immensely entertaining faux-documentaries The Pervert's Guide to Cinema and The Pervert's Guide to Ideology being wonderful examples.
However, if one tries to really understand what he's trying to get at, by means of an all pervading "ideology" as the medium in which everything happens (and we're pretty much like the fish for whom "What is water?" is a meaningless question) by means of some of the examples that do hit home, one is struck by their obviousness. (This is a common criticism of Continental philosphers - they're almost always incomprehensible but on the rare occasion when they're not, they say obvious and trivial things: see this critique in a Noam Chomsky interview for example.)
For example as far as I can guess, Žižek's concept of ideology and its supreme reign in human society is indistinguishable from that of the importance of plausible deniability, maintenance of public appearances, noble lies and in general, of the rather basic fact that common knowledge can radically disrupt the routine behavior of a group of people. Not only are these old ideas (Aumann's seminal paper "Agreeing to Disagree" on Common Knowledge and its implications for Game Theory in particular, was written in '76 and was a complete set-theoretic formulation/mathematicization of this problem) but on their ontological and epistemological characterization and by extension, their application to understanding behavioral aspects of human societies; more has been said, and much more elegantly; by greater minds (in my opinion) than Žižek's.
However, one thing that you can't deny Žižek is how he's taken his brand of obscure (and sometimes obscurantist (!) (though it must be said, he can be very clear, cogent and reasonable, as can be seen here with Charlie Rose: Most Dangerous Philosopher)) philosophy to the level of sublime (no pun intended) entertainment; and for this, he deserves our plaudits.
