If you (a) read or (b) send e-mail, you might want to check this article.
… if we rely solely on e-mail at work, the absence of a channel for the brain's emotional circuitry carries risks. In an article to be published next year in the Academy of Management Review, Kristin Byron, an assistant professor of management at Syracuse University's Whitman School of Management, finds that e-mail generally increases the likelihood of conflict and miscommunication.I've noticed this informally. It's incredibly easy for recipients to misinterpret the "tone" of your e-mail, imagining a totally different attitude than the one you intended to convey. That can be disastrous.
And, of course, it works the other way too. If you've ever received e-mail that you thought was rude, obnoxious, shrill, angry, etc.: your impression may well have been totally off-base. As above, there's a good possibility that your misunderstanding can cause bigger problems, usually quicker than you'd expect.
I also noticed—in my younger days—equivalent symptoms on Usenet newsgroups, where sometimes threads on totally innocuous topics between ordinarily reasonable people would quickly blow up into full-fledged flamewars. I would imagine some blogospheric conflict results from the same thing.
It's easier to offer advice to the reader: be aware of the effect and heavily discount any "emotional vibes" you imagine to be present in what you're reading, especially if you don't know the writer personally.
For the writer: take a second—and maybe a third—look at what you've written before you commit it to your SMTP server. Put yourself at the other guys' keyboard, imagine that you're receiving it.
If you send e-mail in the course of your job, it doesn't hurt to ramp up the professionalism a bit. Also, the politeness: can you work a "please" or "thanks" in there? (My job also allows me to work in "sorry" more often than I'd like.) If you worded something as a demand, you might want to think about rephrasing it as a request, recommendation, or suggestion.
Avoid even the hint of sarcasm. For a bigger challenge: avoid even innocent off-the-cuff remarks that can be imagined to be sarcasm. (Unless, of course, that's what you really want … but you don't, do you?)
I've often simply given up on composing messages I couldn't get "right." That's not an awful thing; sometimes a phone call or "facemail" is a better way to go.
[If you're interested in further reading: here's a short blurb on the topic from Wired last year, based on research described here. Here is an entire book chapter devoted to accurately conveying your e-motional tone, full of practical suggestions. ]
Oh, by the way: you're welcome!