Found a McKinsey study that Cites  a50% Drop in Viewers, 40% Hike in Prime-Time Ad Spend Over Last Decade and by 2010 traditional TV advertising to be one-third as effective as it was in 1990.

"That shocking statistic, delivered to the company’s Fortune 100 clients in a report on media proliferation, assumes a 15% decrease in buying power driving by cost-per-thousand rate increases; a 23% decline in ads viewed due to switching off; a 9% loss of attention to ads due to increased multitasking and a 37% decrease in message impact due to saturation.

"You’ve also got pronounced changes in consumer behavior while they’re consuming media," said Tom French, director at McKinsey. "And ad spending is decreasingly reflecting consumer behavior."

According to the report, real ad spending on prime-time broadcast TV has increased over last decade by about 40% even as viewers have dropped almost 50%. Paying more for less translates into a much higher cost-per-viewer-reached — a trend also true in radio and print. "

But I’m wondering how fair it is to compare 2010 with 1990 as most of the media we use to consume information and entertainment did not exist in 1990 - therefore it might not be fair to compare a decrease of effectiveness in the way the research has done.

"Thank a combination of older technologies such as cable, PC computers, cellphones, CD players, VCRs, game consoles and the internet, along with more recent ones — PDAs, broadband Internet, digital cable, home wireless networks, MP3 players, DVRs and VOD– for those changes. And teens foretell an even more radical shift in future media consumption, the report points out: They spend less than half as much time watching TV as typical adults do. Teens also spend 600% more time online, surfing the web.

According to Forrester Research’s most recent North American Consumer Technology Adoption Study, people ages 18 to 26 spend more time online than watching TV and are adopting new technology faster than any other generation. Because of that, they tend to be more receptive to blog, podcast and mobile-web ads. "

The rest of the article talks about adjusting " reach numbers" ; I don’t as yet have a lot ot say about that subject - only that television appears to be a less and less attractive advertising medium as time goes on and clearly needs to re-invent itself.