Klout is a web service that estimates the influence of Twitter accounts, and can be used for competitive intelligence. There are a number of such services, and Klout is one of the more useful ones, and the data is well presented. Klout can be used to compare the influence of competitors. For example, here are Pepsi and Coca Cola compared, with Coca Cola coming out as an engaged Tweeter, while Pepsi fills the corner of mass broadcasters:
There is a good deal of other information for each Twitter account on Klout: a visit to their website is recommended.