Here's a case study on using Twitter for business as posted in the Webguild.com site. In this example, Coverity has worked with Position2 to interact with people interested in static source code analysis and solutions. It's a niche field, but it enables critical software to function effectively.
Twitter is a powerful tool for staying connected and interacting in a more personal manner. Coverity is one of many clients who are taking using social media to interact with their prospects and customers.