all of the GA lines that I've been in this tour (4 total) have been well-organized and well-run. the fans at those shows (Dublin 2/3, Chicago 2 and NJ 2) started a list, and worked with venue security to enforce it. Everything ran smoothly, and there wasn't a huge problem with line-cutters or anything like that. Sure, we had to sprint the length of a football field once inside the gates, but before then it was pretty organized.
As for U2, it would be great if they could prepare venues for what to expect in advance-- like, weeks in advance, not the day before (or day of) the show. if the venues actually knew what to expect (ie, that fans WILL try to camp out even if they're told they can't, and that there will be a mad rush when gates open), then maybe they'll be better prepared and things will go smoother.
that being said, U2 has never actually done this. i've done a fair number of GA lines over the course of Elevation, Vertigo and now 360. Most have been very organized lines, with just a couple that got out of control. But every single time I've gotten in the GA line, I've realized that it's a total gamble as to whether it's going to work smoothly. It's pretty stressful, especially right before the gates open.
Nevertheless, it's pretty clear that U2 has no interest in getting involved with the GA line-- EXCEPT when they got the brilliant idea to scan tickets for the lottery. And even this scanning occurred only *after* the line had already been organized by the fans on their own, which involved skirmishes with security regarding camping, etc. I really do NOT like the lottery, and would much prefer the first-come, first-served system, but I do wish that venue security was a little more "clued in" by U2 security well in advance, so that things could possibly run a bit smoother.
i know some people have tossed around the idea of using Bruce's system (where a number is drawn at random just before doors, and then that number becomes #1, and everyone else in line gets behind that person). i've never experienced it, but it seems just as random as the lottery that was used on Vertigo, so i don't like the idea of it.