Quote from overrider
From what I've seen so far, I got the impression from the Devs that you won't run into random people while roaming except for towns and group events. I could be wrong.
The impression I got was that you will encounter other players, but they can't influence you. The demo seemed to echo this as well. But I don't know if them not being able to influence you doesn't mean they can't influence your mobs (which to me is directly influencing the player). I know one of the devs mentioned a player cap for certain areas (the whole open zone) and that it isn't exactly a small cap (40 ish) in Diablo terms.