Successful communication in an online environment has two key elements: quality and sensitivity. One ensures quality by following an OP thoughtfully, responding carefully, and providing support through links. Sensitivity involves a collaborative perspective--always expecting and facilitating diversityof opinion from respondents. The most powerful and effective exchange of information is through interactive dialogues--and the spirit of those dialogues needs to be respected. Breaking in on an exchange should depend on whether or not one can move the dialogue forward--or if one can broaden the dialog.
That's my standard at GHMB--the same as when I teach secular online college classes to adult students.