I am one of those holdouts who does not use twitter. Despite people assuring me that I would "get it" once I took the plunge, and despite listening to presentations on the use of twitter, I could not see the relevance to me or the pedagogical usefulness of it in my teaching. Thanks to a fellow participant in #PLENK2010, I found this video that finally explains why I perceive twitter the way I do and validates (to some extent) my feelings on the topic: http://tallblog.conted.ox.ac.uk/index.php/2009/10/14/visitors-residents-the-video/
The visitor vs resident analogy made by David White definitely appeals to me. I like it because it is not an either/or proposition and also because it does help me understand my own preferences for interacting with the technology. It is also takes account of the difference between professional/institutional and personal space on the internet. This is a distinction that I do try to maintain. Although I am on FB, this is mainly personal; a few colleagues who are also real friends, are also friends on FB, but that's because they are already in my personal life.