The context in which an interaction occurs has a profound effect on communication. In face-to-face encounters, factors ranging from psychological to environmental to cultural all have an effect on how the message is transmitted and how it is understood. Online communication is no less subject to context, and may bring with it additional contextual issues that will have an effect on the intended message.
The type of technology being used to facilitate the interaction, for example, has a bearing on the environmental context of the conversation. A conversation taking place through instant messaging in between meetings will have a different flavor than if the same topic were discussed in a virtual world, on the phone, or in an online meeting room.
The challenge of any communication, that of being understood, exists online as much as—maybe more so than—offline. Posts on threaded discussion forums and instant message communications are notoriously hard to decode correctly because of the lack of nuance. As more people participate in these kinds of communications, signals that were developed to add context to text-based messages, like smileys ( :-) ) and tags (like <rant> </rant>), are slipping into the mainstream. The issue of context is far from solved, though, and continues to surface with each new mode of communication that emerges.