Pew Internet & American Life Project: Instant Messaging: "2004 Pew Internet & American Life surveys reveal that more than four in ten online Americans instant message (IM). That reflects about 53 million American adults who use instant messaging programs. About 11 million of them IM at work and they are becoming fond of its capacity to encourage productivity and interoffice cooperation.
At the same time, IM usage varies widely across different age groups. Instant messengers utilize IM not only as a way to expand and remain connected their social circle, but also as a form of self-expression, through use of customized away messages, profiles and buddy icons.
Instant messagers use the expressive tools of IM more frequently than the protective tools that allow them to block unwanted communications. Buddy list management also occurs relatively infrequently, with users reporting adding or deleting buddies from their list no more than a few times a month. "
Via Dave Farber