I have to say I saw this one coming. A new study shows the dangers of "secondhand tv" for children. The idea is that tv is an attention vacuum for young children that delays langauge development.
I figured this one out pretty early with our kids. TV is hypnotic to young kids, and as I've written about before, there is no evolutionary mechanism to "turn off" attention to modern technology. So even if the tv is just on in the background, it's having an effect.
I can't wait until they continue this line of research and show that computer use by young children is just as detrimental. (I thoroughly believe it is, but it will take a while for science to overcome the supposed "educational benefits" of computers for young children.)