Hi folks, I'm a recent addition to the list... couple thoughts to add into the mix: First, Barry's 500 followers seem entirely sensible, given his status as a known author. I would postulate that there are four main avenues for picking up followers on twitter. (1) address book search. If I recall correctly, this is integrated into the system, such that when a new user joins twitter, it offers to search their address book and give them the option of following any matching profiles. That set of users will approximate one's social network and/or facebook friends list (perhaps only loosely so). (2) famous names. Extrapolating from personal experience, I know when I joined twitter I looked over the "following" list of a close colleague with overlapping research interests to see who I should add. Any author whose book or article I had found particularly interesting was immediately added. This set of users are where I derive much of the added value from twitter, personally. Without them, twitter isn't *much* different from facebook status updates. With them, I can learn about interesting articles and emerging topics beyond my network of close colleagues. (3) retweets/in-tweet mentions. I pick up a few additional followers after every tech conference, and they are often people who aren't attending the conference. This is because I'll be mentioned or retweeted by a colleague with a much larger following. The retweet mechanism is probably the most important for modeling/understanding the development of twitter norms, I think. Those who solely tweet about their lunch will virtually never be retweeted. Those who offer humor, valuable links, or 140-character insight will be. Humor and insight, in particular, likely encourage additional followers. Institutions like #followfriday are an outgrowth from this class. (4) offline mentions. If Barry includes his twitter handle on the first slide of a conference presentation, he likely sees a few immediate adds. When CNN, Oprah, etc announce their twitter handle to a mass audience, that both spurs an increase in twitter accounts and a surge in followers. I personally haven't partaken in these sites, and have little to no sense of what to make of it. There's a fifth category, which includes spambots, advertisers, etc, but I think we can safely set that aside as noise for the moment. Another dynamic to consider in any modeling exercise (and one which will be a HUGE pain for any empirical studies) is variance in platform. I use the iPhone app "tweety." Barry uses tweetdeck. It sounds like these platforms have different functionalities, and the growth of twitter will only encourage further code-based innovations of this sort. Compare those to twitter-via-laptop or -desktop and you have a completely different user experience. I never used twitter until I downloaded tweetie, because I found it a less-appealing distraction than facebook and a couple of favored blogs and discussion boards. With the mobile client, I now check twitter while waiting in line for coffee or sitting at a red light. Mobility and platform have a huge impact on how I'm experiencing the medium, and that in turn shapes my normative opinions about how people should and should not use the medium. Very interesting topic, thanks for raising it! -Dave Karpf -- Dave Karpf PhD, Political Science University of Pennsylvania Postdoctoral Research Associate Taubman Center for Public Policy Brown University www.davidkarpf.com davekarpf@gmail.com