Awesome thread, Guys. Cram, brilliant OP, and the comments here are golden.
Nonsense seems to have a bullshit test that makes the (to borrow from Cain) "holistic" part of it what's salient and therefore gives it some oomph or momentum within whatever target or audience it has. The lack of this salience is what in general sets off the bullshit meter. LMNO's example of "Jabberwocky" is so apt, it's awesome. (only poem I know in its entireity, more's the pity)
I do believe the routinization of our brains, and what makes that routinization so attractive to them, is what makes the saliency so important for nonsense to be effective. "Radomness" seems to be the "hawt" item of the nowaday, and I can't say that most things that seem "random" are actually thus. In fact, the well-read consumer (and for an American, that's just someone who pays attention to our bullshit news programs and maybe a few fringe ones) will never view anything produced by anyone as random every again. The focus-group-statisticianized-pollster-generated-figures-charts-and-percentages neo-neo-post-post-modern age seems to have created a nonentity in randomness.
But that people can recognize randomness, and not see it as 1) the Devil 2) God 3) another deity 4) their neighbor (eh, this one is still being worked through) but rather a pattern in the universe or something imposed on them by a big corporation is a large step into figuring out how we can be manipulated.
So this idea of a salient or recognized nonsense that shocks you out of your normal routinization becomes more important and actually I think less irrelevant, especially when you think where memology in the internet, the "big brother is being watched" phenomenon of the video cell phone + YouTube access, and all other bottom-up ways of introducing the Dadaist, formerly-left-field but now rather kitchy field of WTF? might lead to.