Summary: We tend to view communication using social media, online tools and web sites, IM, chat, SMS, and so literally. Messages have authors, what they seem to be saying is what they in fact mean to say, and so on. The reader is the interpreter of what's communicated. But the medium not only transmits and enables talk by capturing communication on web pages, in chat and IMs, in emails, blog posts, and comments. It also produces the author: as an appearance or effect of the medium. This is enough to go on in most cases, but it does have implications. We do not "exist" online any more than a Second Life avatar exists in the real world. These are media of production. Presence, talk, intent, motive, character, personality.... all these are manufactured by the social media that are their means of production. HCI and human factors research has a deep field of study in social media.
It would seem that asynchronous technologies of communication, by bracketing physical place and context from the interaction, render it irrelevant. But context still plays a prominent role in many online and other kinds of interpersonal or community interaction. It does it perhaps more through language and conventions established by the participants involved. Any online community with enough history will have a character of interaction, and unspoken conventions that help its members second guess each other's communicative intentions. Asynchronous technologies require users to be explicit about context that everyday interaction simply provides implicitly. We cannot say yet whether this is a side effect of learning how to use a medium. That until we have developed familiar and recognizable cultural practices, we are required to state and make them by explicit means. Until we do know, we can only inquire into the observations we're able to make about the function of context in asynchronously-mediated interaction.