Tens of millions of Americans have purchased Apple's iPad digital tablet, and all of the major television networks have designed free apps for it to allow users to access a limited number of their TV shows. But so far no one is quite sure how many people are actually using those apps, which programs are being accessed, and -- most important -- how many commercials are being viewed and by whom. Neither does anyone know how much time consumers are spending searching the web or merely playing games on their iPads. On Wednesday, Disney/ABC Television Group's ABC Research team and Nielsen Media Research announced that they were launching a joint effort "to substantially improve understanding of how people use iPads for video consumption and other activities." About 200 consumers agreeing to participate in the study will have their behavior on the iPad monitored via a downloadable meter "which will measure reach, duration, frequency and page views of their iPad apps and web usage."