NBC is reporting a boost in ratings for “The Office,” one of 12 NBC shows available for download from iTunes to an iPod. While some experts are skeptical that the source of the boost is indeed the video downloads, other experts indicate that the young-adult audience, a major demographic for iTunes and the iPod, is much more responsive to on-demand entertainment and represents a new additive audience.

So what does this mean for the advertising world? It means many of the old assumptions and paradigms are on their way out. We’re using the example of TV but this concept applies to media in general.

There is no guarantee anymore that your viewer is sitting on the couch in front of the television. You can’t assume that they’re viewing the episode at dinner time, even though the episode originally aired at 6:30 p.m. For all you know the viewer is riding a bus to work at 7 a.m. so running a spot about a shrimp sampler platter might turn the viewer’s stomach rather than entice them to make a purchase.

This on-demand phenomenon, where the viewer decides what to watch and when to watch it, is happening to the Web as well. RSS (previous article) allows people to “subscribe” to your website’s content. They don’t actually have to type in your URL to see if there is anything new or interesting.

The value of your home page to these users is greatly diminished because they’ll have a list of links regularly delivered to them and they’ll just pick and choose which links to click, effectively bypassing the whole “experience” of navigating around your website.

One final key point is to recognize that the technologies empowering this on-demand phenomenon (RSS, blogging, audio and video podcasting, etc.) are also making it possible for more and more people to create and deliver content to a broad audience. With very little money, for example, you can create a video or audio file which can be downloaded by millions of people via iTunes. Advertising is already finding its way into these “home grown” sources of content and if you’re willing to dive in, you can give your clients a head start.