The advent of the word processor spelled the doom of the professional typist. An entire industry was distrupted. We all know that the mass adoption of the Internet in the early '90s put the writing on the wall for newspaper and traditional media businesses.
However, something that I had never thought through was how the development of social networking and linked blogs was disruptive to classic marketing and pr. Even at DTLink Software, we have noticed that what used to work just a few years ago no longer does.
I just finished reading The Purple Cow by Seth Godin. In it he makes some very interesting assertions about how modern day marketing has changed fundamentally and provides some surprising case studies to support his positions.