... Though e-mail is a powerful and convenient medium, researchers have identified three major problems. First and foremost, e-mail lacks cues like facial expression and tone of voice. That makes it difficult for recipients to decode meaning well. Second, the prospect of instantaneous communication creates an urgency that pressures e-mailers to think and write quickly, which can lead to carelessness. Finally, the inability to develop personal rapport over e-mail makes relationships fragile in the face of conflict.
In effect, e-mail cannot adequately convey emotion. A recent study by Profs. Justin Kruger of New York University and Nicholas Epley of the University of Chicago focused on how well sarcasm is detected in electronic messages. Their conclusion: Not only do e-mail senders overestimate their ability to communicate feelings, but e-mail recipients also overestimate their ability to correctly decode those feelings.
Here's the link to the story by Daniel Enemark in the Christian Science Monitor.