PUGging in WoW -or in any MMO to be honest- is pretty ugly, really. In most cases people are running the instances only for their own personal agendas and gains, with no interest of their companion's interests at all. As it happens, the current state of PUGging in WoW is even worse: the people running in PUGs don't have the best interest of the PUG in their interest, either.
There is also the problem with performance. Bob Turkey posted a nice post about the current state of play depicting the problems of gearscore addiction in the game from the eyes of raid PUGging. People are so concerned over the raid performance and their own ease of play that they rely on an arbitrary number instead of common sense. If you have the achievement, you surely have the skills to pull it even though your gs might be below the arbitrary boundary you set up. And if you're already performing better than the people with required gs, you sure as hell are carrying your weight, right?
My recent experience with the DK not willing to run Halls of Stone because he didn't know it prove this: being concerned over the performance resorts people running safe and 'easy' instances and doesn't push them to learn their class.
What does this do with the trust I mention in the title?
A lot. The raid leader of a PUG raid uses the arbitrary gs number to evaluate the people s/he takes on the raid because s/he cannot trust the achievement or the word of the player. They want to have a solid run for the gear they seek, not wiping because of the weakest link. The DK couldn't trust he wouldn't be kicked from the group if he messed up because he didn't know the instance. I don't want to tank because I have this feeling that the people I'm running heroics don't trust me. And I enjoy running with my shadowpriest because I can trust the tank doing his/her job properly, as I never question their ability to do so.
I feel that there is a real question of trust involved in WoW, or lack of it, really. People run their own personal agendas in such a way that it would be quite the same if the rest of the 5 man group in an instance were just AI bots. You cannot trust the other players in any way, because they are either ninja, don't know their class or don't know the bosses.
There is no room for failures, nor no room for learning. Which usually requires failures to happen, really.
I trust the tank in the group to be the one who keeps the harm out of my way when I play my priest. When I play my tank my job is to keep the mobs pounding on me, trusting that the healer keeps me alive and the dps keeps their threat throttle at reasonable level. And as shadowpriest I make my darnest to keep the mobs on the tank, never jeopardizing his aggro over them.
Whenever I play in a group, I'm willing to do everything for the group. I trust the players I play with, and I want to believe that they will do their best like I do.
But I seldom feel trusted by them. How about you?