There are actually frequent cases of highschoolers taking IRL bullying onto facebook, so...geography certainly doesn't turn off nasty behavior.
What DOES have a known effect is the number of people you're interacting with:
http://en.wikipedia.org/wiki/Dunbar%27s_numberSo...somewhere like the DL where there's less than 150 people who could be described as being DL regulars, you tend to form stable relationships instead of treating people like strangers. (And I don't think the DL became more or less civil after DLcons when we actually met each other and knew IRL names).
Sample bias at play here in my opinion. How much more mean on the internets am I than in person as a counter example?
Some people turn into an introverted ball IRL, but are decently outspoken on the internet. I'm a little like that myself. The internet lets me be solitary and write an essay--and maybe 10 people would read it. But I don't enter a social gathering of 20 people and start telling a story while most of them listen--I'm too introverted for that. So...IRL I sit politely and listen.
Doesn't mean that I'm not thinking stuff I'm not saying when IRL, or that if I was more extroverted I might say some of the stuff I'm thinking. (The example jumping to mind is my extroverted sister, who tends to pretty much think out loud).
