This cracks me up. It cracks me up because it hints at a very deep truth — the struggle to use written text in a way that adequately communicates emotional content. Never before have we had this near-instantaneous interpersonal written communication. Never before have we conducted so much business and navigated so many relationships in a written medium.
When someone reaches for that caps lock key, they are emotional and they want to holler at someone. They want the text to holler for them. And it does! We add the emotion back in when we read it.
Think about it — we lose information when we type an email message and that information is put back by the recipient, using clues from the text. Things like italics, bolding, case and punctuation, in addition, of course, to the word choices in the message, try to convey a multi-dimensional interpersonal communication over a single, written channel. The emotional content of emails is often (some might say always) misinterpreted by the recipient.
Except, perhaps, when we unleash the fury of caps lock.