Been playing this game for a bit over a month, actually, but did SWG for quite awhile followed by a WoW stint from Lich King til just after Cata. Thus far I have had mostly positive group experiences - a few negatives, but that happens. Honestly, I just don't care that much - if a player is willing to loot in a way that gets them on too many ignore lists to even get a group anymore, then fine.
So they ninja the chestpiece that I did the run for in the first place. IMO, so what? I'll just run it again, I'll have an easier time finding another group than they will - I'm heals, after all