In my experience, for communication with people (including myself) using dialup or intermittently connected in some other way, the on-/offline indicator on ICQ

In my experience, for communication with people (including myself) using dialup or intermittently connected in some other way, the on-/offline indicator on ICQ was a killer feature, an indication of availability and responsiveness that required no effort to maintain, and I have not seen it usefully reproduced in the always-connected broadband world. Of course, various third-party clients providing “stealth mode” were abundant, so it’s not like this mode delivered everything people wanted out of the box, either. (It might be that the actual important difference was that you used ICQ for casual conversation only, and adding an acquaintance to your contact list was not a given or socially expected; not an implementation or UI issue as such.)