Well, I don't tend to play a lot of RPGs, it's just that Morrowind was one that I really got into - I think it was probably because Morrowind wasn't so much about one linear story and a set of stock characters, instead it was so much about creating your own character and having the freedom to create your own story. I tend to play strategy games much more often, and I'm sure that these have really helped my decision making, planning, management and tactical skills.
With RPGs, I think that there's a certain amount of imagination needed to play them, so it's really only people who can think in a certain way who will enjoy them in the first place - a lot of people just don't understand how fantasy (be it in books, films, or games) can be interesting. I'm not sure that playing RPGs really affects a person that much, since a lot of any RPG is about the story, so in that sense it's not too different to reading a book, just more interactive.
EDIT: I really doubt that RPGs make people more violent - since you'll be killing magical beasties most of the time it doesn't really relate to the real world

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Anyway, how can RPGs make us less sociable - if it weren't for RPGs, we wouldn't have the W4O community!