I recently read Joel Comm's book "Twitter Power" and got to hear him speak on a short webinar
Having used twitter since November 2006 (www.whendidyoujointwitter.com) I already had a good deal of experience using it and so was interested to see whether the book had anything new to add for me. The quick summary is that yes it did. My use of Twitter has been very much as a social networking tool to keep in touch with people I know and also a convenient way of updating status and having it echo through to my facebook profile. What I took from Joel's book was a very different perspective that helped me to see other ways that Twitter could be effectively used. For me I think the main thing I took away was a set of thoughts around how I could be more intentional with my use of Twitter.
His book also includes some thoughts on steps you can take to increase your following. One of the suggestions being to engage in conversations through twitter. If someone replies to you then that will appear in their Twitter stream and some of their followers may then go see who you are and follow you. I can vouch for the validity of this approach having sent a tweet to Joel after the webinar, got a reply from him and then saw my follwer list rise by 15 people over the course of the next day.