David, I can't say you're wrong, but how can you criticize Johnson's anecdotal, correlative data and then turn around and write, "students in Russia and some European countries have consistently outscored US students on all sorts of scholastic tests. And they watch TV and play computer games less in those countries." That's correlative and presumptive data if ever I've seen it.
Pointing to the general stupidity of our youth sounds like a good argument against Johnson's thesis as well, but it's a bit of a straw-man in that it assumes that prior to the advent of these pop culture media (and content,) absolutely everyone could make perfect change off the top of his head, or was fully aware of the Bill of Rights and its nuances, etc. Stupidity is not new to society in any way, though we are now more adept at tracking it. I haven't lived in the United States for awhile but I remember a recurring segment on the Tonight Show with Jay Leno wherein Jay went around Los Angeles (and, I presume, other cities) asking extremely basic questions (state capitals, where certain wars were fought, etc.) and mocking the many people unable to answer them. I also recall that these rubes varied widely in age, which suggests that either stupidity gleaned from video games, reality TV, etc. is indifferent to age, gender, race, education level, and actual consumption of said media, or that some people are simply bad at remembering things and/or less intelligent than others. I think that if there has been a decrease in general intelligence it likely has more to do with educational systems as well as an inability of said systems to adapt to, and utilize new media. For example, as an Atheist, I genuinely believe that certain Southern US States laws against teaching evolution as fact (and thereby allowing creationism to be taught as valid science) is far more detrimental to children's collective intelligence (not to mention the role of the government.)
The best counter-argument to Johnson is the shortening of the attention span. As a massive fan of the West Wing, I can certainly stay engrossed in that show for hours on end, though I will often "multi-task" throughout, which means that, much as I love the show, it cannot (or, I suppose, does not) capture my attention fully.
That said, I'm a product of Neil Postman's, "Amusing Ourselves to Death" dystopia (age 25), having grown up on video games, TV, and the internet, and have read James Joyce's, "Ulysses" twice*, so I suppose the demands of a media product (regardless of medium or era) dictate my personal attention more than the medium itself.
Anyway, I enjoyed the book, though I admit there are certainly holes in some arguments, I just feel that David displayed a bit of the "knee-jerk" reaction to the idea that these things could be positive that is not only unhelpful, but the exact reaction that Johnson asks his readers not to have.
*This was not meant to be self-aggrandizing, merely a comment that with all the damage to the attention span I was able to read what is considered one of the most complex novels ever written. **
**Never got through "Finnegan's Wake" though...