Usability is defined as making websites more usable, useful, and accessible to your target audience. Although there are thousands of web developers there are few who are experts in usability. When you begin to think about either building or improving your website be sure to consider how you want your users to interact with the website and define some specific goals you want your users to perform. Here is an article below that considers usability and the social web.
Rethinking User Research and Usability Testing for the Social Web.