So far I've only had one bad experience in this game while part of a pug. It was on one of my alts. I joined the group in progress, they were on the last boss in Hammer Station. The tank was going on and on about noob this, and noob that, and how the last two dps were horrible. He was the first player I've put on ignore in this game.
Everyone else I've had the pleasure of grouping with, in the group finder, doing dailies, just running around, has been great. The Harbinger has some good people on it.