A Business Strategy for Using Twitter
Ogilvy has a simple diagram on how twitter can be used as part of a PR strategy. The gist of it is simple: monitor and follow people who are either your target market or people who can influence or affect your business.
After which, create tweets which help to fulfill a specific purpose and be sure to interact widely by pro-actively engaging other users via replies or direct messages. Simple enough and it shows the basic framework for how Twitter can and is currently used by savvy businesses.