Wired has posted this piece by Steven Johnson linking the "Flynn Effect"—the gradual increase of the population's aggregate IQ over time—to new media consumption. Like his much-discussed recent New York Times Magazine piece, it's based on his forthcoming book Everything Bad is Good For You.
I'm generally sympathetic to the thesis, and not a hardcore skeptic about IQ or "general intelligence," but I think it's worth bearing in mind that at least part of the way new media make us "smarter" is by shaping our concept of intelligence at the same time as they train us in the skills and behaviors that match that concept.
Neal Postman used to like to cite the example of Solomon (I think it was Solomon, anyway; I'm too lazy to check right now), who was considered wise in part because he had memorized some huge number of maxims. Now, having such a huge maxim-cache might today be considered impressive in a parlor-trick sort of way, but because pervasive external information-storage makes that sort of thing unnecessary, we'd hardly consider it a crucial test of intelligence. We're more apt to be impressed now with someone who can quickly navigate and apply all that stored information. New media inculcate the kind of on-the-spot problem solving intelligence Johnson talks about; they may not do much to develop the different kind of intelligence exercised by, say, reading and thinking about Socratic dialogues or doing a close reading of Proust or Joyce.
That's not to say we ought to buy into Postman-style luddite alarmism. If new media restructure our concept of intelligence, it's in part because they provide us real benefits and make the skills required to navigate them genuinely valuable. But it's worth recalling that the technology is, to some extent (because, of course, "problem solving" intelligence will already be an important part of any conception), advancing us toward a target that it placed there.