Having worked many back stages at many venues, I agree, its really nothing special.
At the Boston Garden(and most arenas) it is a warehouse type area off the floor level that leads to a furnished hallway. The press room for the hockey and basketball games is catering, sometimes by a local company hired by LiveNation, sometimes by tour hired companies.
Turn and go down the long locker room hallway, and you will see various rooms used for sports converted to tour offices, dressing rooms, promoter offices, etc.
Bands often designate a room for reception, be it the "round room" or "the lounge" or whatever you want to call it. Unless the band is looking for you and others in a specific area, or you are ushered into their area by tour staff, mark my words, you will not run across them. I worked 80 hours last weekend in Foxboro, mostly backstage, and never saw any of them. I got lucky once working in Somerville, a VERY small venue where you couldn't not run into them.
There are usually about 8 security positions backstage for a band like U2, all of whom are staffed by people who look very passive reading their newspapers or books, but will most certainly look up from this when someone walks by them. It is very easy to tell when someone is supposed to be back there without even looking at their pass- body language, attire, etc. Most security know the local crew, have seen all of the tour people and family/friends walk by numerous times before doors open to the public, and by the time the show starts, know cold who should and shouldn't be back there. Some companies will ONLY put this kind of staff member in the backstage area for a high profile show. Think clean cut, in shape, capable of taking someone down AND carrying on an intelligent conversation, hold a respectable real job and do security for part time fun, not the meat head goons you see on the stage barricade.
I see very few corporate type events, did not even see any backstage for Blackberry this tour. Maybe these were more prevalent in a time period when the economy was a little better and showing off your U2 backstage pass to clients that came in was an affordable luxury. Since I started in security, the economy has gone from shaky(2006) to the tank(now). I do however, see alot of meet and greets, etc. Often a meet and greet will have their own special stick on passes, and are only allowed backstage pre or post show(whenever said meet and greet takes place) and may only move about with an all access tour person.
Backstage passes are 100% controlled by the band, and are the only way back there. I hate it when people ask me if I can get them backstage, just because I am security. What they don't understand is that there are different levels of backstage pass, only the highest (usually all access) of which is allowed to escort anyone else backstage. Different levels have different privileges- for example, a local crew member would never be allowed in a dressing room or backstage during a show. A local security person does not determine who can go backstage to do anything, nonetheless meet the band. Getting someone in a venue is something I have done , getting someone moved in seats, I've done that before, getting someone a GA wristband for a certain show, I've done that before too. However, I would never even consider trying to bring anyone backstage. Even if I tried it, tour security would have alot to say about it to me and my boss.
I have a pass sheet from 360 and will try and scan it if I grow a brain in the near future. Its nothing special, and was truly limited this time. There was a "Tour Personnel" pass that functioned as an all access, a working pass for local crew, a VIP pass(I think) and a Guest pass, for members of snow patrol, their family, other special guests, etc.