Importance is a fundamental part of how we function in society, but it is rarely understood. The timeless "How to Win Friends and Influence People" does an excellent job explaining importances' role in self-esteem and growth.
Simply, importance is the value of contribution and expertise to the community. Linus Torvalds importance to the Linux community is apparent to many in a subjective way, yet determining his objective importance is currently not possible.
Systems, such as Amazon.com's platform, are becoming far better at valuing and sorting content based upon the level of contribution of an individual and the level of interaction and support that the viewing community gives the contributor. Ultimately a contributor's importance will determine how his (her) content contributions are presented to the viewing community. Important contributor's content will appear higher on the page and be used in many more locations.
Communicating the importance back to the contributor will create a positive feedback loop wherein more quality contributions will lead to higher placement of all contributions. This expertise that is conferred by the community supports and individuals need for place and importance in a given community.
A Backcountry.com page that displays usage of importance in reviews and questions and answers