So anything that pops up on the screen should be directed to that ONE person who's reading it. With rare exception, people don't buy magazines, listen to radio, or watch television for the ads. They want information or entertainment - and they also read, watch, or listen to ads when something in the ad catches their attention. In the 1950s, people watched even test patterns on television. The novelty is gone.
Some folks stare at Web for hours at a time just because it's interesting .
But that will change. The novelty will wear off. This is true of all new media. It happened with radio. It happened with television.