Marketing, I think, can be divided into two eras.The first, the biggest, the baddest and the most impressive was the era in which marketers were able to reach the unreachable. Ads could be used to interrupt people who weren't intending to hear from you. PR could be used to get a story to show up on Oprah or in the paper, reaching people who weren't seeking you out.
Sure, there were exceptions to this model (the Yellow Pages and the classifieds, for example), but generally speaking, the biggest wins for a marketer happened in this arena.
We're watching it die.