We're barely into the second decade of the the Net's development. Unlike the first ten years when corporations built the web, over the next decade the Internet will largely be created by the people for the people via online communities.

This means that the phrase "public relations" is (finally) taking on a literal meaning. It is our industry's charter to help clients navigate online communities and build authentic, meaningful relationships with their stakeholders. However, the challenge is if you blink, the entire vista will change.

Most marketers prefer to gravitate to the big hubs. These include Edelman clients like MSN Spaces and MySpace, as well as Facebook, Bebo, LinkedIn and a host of others that have lots of eyeballs. Any of these sites can serve as strong venues for marketing programs.

What we take for granted, however, is that they will be around in the long term. On the Internet, churn is constant.

Historically, online communities have perpetually come and go. The Internet Archive amber is littered with fossilized communities that once dominated, much the way the T-Rex roamed during the Mesozoic era. These include former stalwarts such as Angelfire, The Well, TheGlobe.com, GeoCities, Tripod and Friendster.

Only a handful of community sites over the last dozen years have had staying power. If you study them you'll find moats to protect them from competitors and fickle users. These barriers to entry include peer-to-peer commerce (in the case of Edelman client eBay), robust user reviews (Amazon.com) and deep entrenchment in vertical markets (BlackPlanet.com).

The online universe is about to grow even more complex, making it harder for some sites to maintain their dominance. Over the next several years social networking and community will become less about specific venues and more of a river that runs through the entire web. As Cisco's Dan Scheinman says, community will define not only how content is created, but also how it is consumed.

This means that although it will get harder for marketers to achieve scale, community engagement will become a much more efficient and effective way to engage an audience. This requires a shift in thinking though as community becomes like running water. The takeaway here is never bet against change - it's constant on the web.