Social networking sites present very important opportunities for advertisers who are willing to play ball with their audiences. These sites are in the business of aggregating what many experts are calling "naturally forming communities," many of which will voluntarily coalesce around particular, narrowly specific content and interests. These social networking sites attract a generally younger crowd of people who are unusually receptive and who tend to be more interested in self expression than the average online consumer. Advertisers that are willing to give up absolute control over their brand and their messaging can learn to leverage these communities by opening themselves to, and engaging with, these like-minded groups of people.

Different social networking sites tend to have different strengths and weaknesses, in part attributable to their differing origins, functionality and perceived images. For example, MySpace reaches a lot more people that some other social networking sites, and also gives its users more control over their own pages. This results in the site attracting large numbers of people who are comfortable with a higher degree of self-expression and a deeper level of interpersonal communication.

In addition, MySpace began by offering independent musicians and bands a place to make themselves known to larger audiences, and that has carried through its growth, which makes it particularly suitable for advertisers in the music industry.

Facebook has its own strengths for advertisers, including allowing deep access to very granular niches where you can find people who will be deeply concerned with a subject that relates to your brand or product. You can instantly find out how many Facebook users meet your interest-group criteria, such as "living in London" and also "interested in Britney Spears."

On the other hand, Facebook is less flexible than some other social networks when it comes to meeting special needs of advertisers. Ad units are heavily standardized, video advertising is locked out and you can't skin your own page on Faceback as you can on MySpace and Bebo.

It's much the same with entertainment industry sites like "People.com" and "ew.com."

"People.com" is often said to be more like the industry gossip magazine. It's full of what they're wearing and who's marrying whom, while "ew.com" is usually considered to be more of an entertainment industry newsletter, providing information in a more "work-oriented" context. Knowing who you want to reach and what message you want to convey, you can pick and choose among the strengths and weaknesses of various sites.