I've never had a problem with U2 security staff, but their staff only follows the band around so they have very little effect on how things go down. The venue staff is responsible for everything that happes with the GA lines, monitoring the venue in general, and standing down on the floor around the stage areas.
In my experience, Chicago is the absolute best venue in terms of how fans are treated. The director of the UC came out and told the patrol cops that we were allowed to camp outside the venue and were not causing trouble. He also unlocked the parking lot so we could use the porta-poties. During the shows, he came on the floor and passed out snacks and water bottles. At one show, there were tons of people trying to cut and push us around. Technically, the venue security does not honor the fans' system for lining up, but it got out of hand and the big guy at the front said if he had to, he would start enforcing our numbers. He said that their security respects the numbering system of the fans and he expects everyone else to have the same respect. Mostly, it's rich yuppies that show up minutes before and start whining because they thought they could cut in front of people who've literally been in line for days.
Auburn Hills was the worst. They did not let people line up until 2pm the day of. Then, they let all these other people cut because one entrance opened slightly before 2 and everyone else who spent the night across the street was lined up waiting at the main entrance as we were told. They don't pay any attention to the numbering system. The first night, I went to the front of the line, OUTSIDE of their little fence, to say hi to people and these guys started yelling and pushing me around. I said "Hey, I'm just talking to friends, I don't even have a number on my hand!" but they threw me away and said I tried to cut. They don't let you use any bathroom, instead they tell you you have to run across this 6 lane highway to find a restaurant. They're constantly yelling at people for no reason, but then ignoring complains when others really are pushing people around and cutting. They have no clue about the policies of the band. For example, like I said they kept harrassing me about the camera until we explained that the band's policy is you can have a non-professional camera on the floor. Then, they decided my camera was too professional looking, even though it's a digital point-and-shoot just like everyone else's (it's a bit larger b/c it has a longer lense). On the floor, they were always scowling and rolling their eyes at people, like we were shit for wanting to see U2 and have a good time. In contrast, we would always make small talk with the floor security in Chicago, and they all seemed to enjoy the shows and weren't bothered by fans.
Pittsburgh was fine with me, but I was one of the first 4 people in line and I heard it got rowdy farther back and they weren't doing anything about it. I think it was a harder venue to monitor b/c it's right downtown so there's a lot of pedestrian traffic and the GA lines are right out there on the sidewalks. Basically, we showed up at 10pm and there was one guy doing the night shift in his booth at the GA entrance. He said we could start the line right there. He even let us order pizza to his booth and use his power to blow up an air mattress. Before bed and at breakfast, he took people in to use the bathroom.