From the current issue of the Economist and their special report on advertising and technology - Leaner and Meaner: Technology has made life harder for admen, but they will not disappear:
"Digital media are much bittier and the pace is much faster. Brad Jakeman of PepsiCo, a drinks company, says his firm used to give agencies between four and six months to produce a piece of content and would pay between $700,000 and $2m for each of them. "Now we need an agency that can produce content in days, with each piece costing $10,000-15,000," he says. Clients are also working with fewer agencies. Until fairly recently General Motors was using 70 agencies to advertise its cars: now the number is down to three."