In the "old days" you focused your planning on an initial demographic target, such as men 18-24 years of age, with HHI $35k-$50k, single, etc. These breakdowns of demographic data would tend to lump together groups of "like-minded" individuals. However, in today's world--where information and trends spread like wildfire through digital media--we are quickly creating a global society where traditional barriers such as race, age, and region are no longer important. What happens as a result of this globalization is that traditionally disparate demographics are latching onto similar trends and ideas, and groups of "like-minded" individuals are truly organized based on their minds--their psychographic information.
For proof that psychographics are becoming more important, we need not look far. At the most recent iMedia Summit, a highly informative presentation broke down the Urban Audience into seven unique segments that detailed subtle differences within each group. Some segments skewed slightly younger and were more of an influencer audience, while others may have skewed to the same age range--but based on geographic data, they may have been slightly later in adopting various trends. Companies like Claritas offer excellent insight into similar audience breakdowns with their Prizm Cluster product. These Clusters group various segments of society together based on the types of music they listen to and the types of clothing they buy.
The reason that psychographics are becoming more important than demographic details is that they focus on behavior. Behavior is what defines an effective campaign. To develop an effective campaign, you must know how the consumer interacts with your messages when they see them, and in what context they see them. You need to convey a message that is relevant to them at any given moment, or will be able to influence their decisions at a later date. Demographics assume that everyone in the group is of the same mindset, but this is too much of an assumption to be effective. You need to know and you need to be flexible enough to react based on their behavior. Demographics are too rigid, and do not take into account the intricacies of human nature.
Think about it... are all 30-year-old men the same? Are all 30-year-old men in New York City the same? Are all 30-year-old men in San Francisco the same? Of course not. Within New York or San Francisco, you have a wide variety of 30-year-old men. Some are career-focused, while some are free spirits. Some are into hip hop, while some are into garage rock or electronica. Some are gamblers, while some are not. The typical stereotypes that might be associated with demographics fall to the wayside when information can be shared in a global community and your personal interests can be affected by a wider range of inputs than what you can see in your immediate vicinity.
What this means for media planners and communications planners is that you need to look much deeper than demographics in order to develop an effective campaign. You need to get into the mind of your audience and hypothesize about their patterns of behavior. You need to understand what they are thinking and which outside factors may affect their decision making from day to day. This also means that your plans need to be dynamic, and must be susceptible to change. The audience is becoming more fickle and reactive to the world around them. Get access to as much psychographic data as you possibly can, and try to crawl into their heads. Then your media plans, and the creative that is tied to them, will be more effective.
Good luck--it ain't gonna be easy!