From the San Francisco Chronicle by way of Boing Boing:

New smart billboards sniff your radio-preferences from leakage from your car and tailor themselves to your taste. The next generation will network with one another to chase you from one segment of the road to another. The billboards -- in Palo Alto, Daly City and Fremont -- will pick up which radio stations are being played and then instantly access a vast databank of information about the people who typically listen to those stations. The electronic ads will then change to fit listener profiles...

For example, if the freeway were packed with country music listeners, the billboards might make a pitch for casinos. If National Public Radio were on, the billboards could change to ads for a high-quality car or a gourmet grocery.

This reminds me of a suggestion from one of my professors at Southern Tech that the Nielson rating system could be replaced by vans driving around neighborhoods monitoring the signals leaked by the local oscillators in the televisions (or set top boxes) to detect the channels being watched. I suppose Tivo and ReplayTV are showing that in the digital age even the vans are not necessary since the viewing habits are recorded by the devices sent to the marketing departments. Instead of having to spend money to collect the viewing statistics, the companies have actually managed to get consumers to pay for this 'benefit' of the system.