To me, saying "Tag clouds are symptoms of the decline of symbolic efficiency" is like saying the Dewey Decimal System (DDC) was a symptom of the decline of symbolic efficiency. Both the DDC and SEO data (this is what tag clouds are a visualization of) are systems for guiding people to information that they are looking for. The DDC is, in fact, a far more constrictive system for organization, forcing any item into only one of a set number of pre-defined categories. SEO data allows for organic categorization, context comparison, and relevancy searches, giving authors more rather than less control over how their content is categorized, and how difficult or easy it is to find.
Thanks to Dale for pointing me towards Thomas Burke as to where he's coming from with a lot of this. Obviously, Jodi Dean is coming out of Zizek with this symbolic efficiency stuff. If there is another source I'm not picking up on it. And I'm sure that Dean has read a lot more Zizek than I have, but it seems like she's looking at what tag clouds are on the surface level, and not what they are in context of SEO being the most efficient, dynamic, and organic way of searching and retrieving information currently in use (far more "efficient" than web-crawlers and meta-tagging, two previous methods of organizing search data). The whole thing seems a little silly to me in light of every other method for mass organization of information in the last, say, few thousand years or so.