fmattyh,
Numbering was not designed to allow people to leave for hours, just to make sure everyone had their proper place in line on a first come first serve basis. There might have been exceptions that I was not aware of, but people did not leave and come back at 5pm, because it would not have been accepted by the fans around.
The cool thing is you get to know the people around you in line, so they can check your spot as long as you don't leave for too long, and there was actually very good 'self-policing' from the fans in terms of people trying to jump the line. It was just not accepted, but the list and numbers helped with that a lot.
At some venues, the security didn't care about our numbering system, but most times they actually did, and made sure themselves people were entering in order. Other times, the fans organizing the list would go through the GA line about 1 hour or 2 before doors would open to make sure everything was in order and no one had jumped the line. When a list of names was used (that was later in the tour) it was even better.
It's certainly not a perfect system, but I found it worked well during Elevation (apart for some abuse by a few fans maybe).
What basically happened in the GA line is that for most of the day, it was pretty easy going, with people sitting down, walking around, hanging out and having fun. But you couldn't come in the morning, leave all day and just come back at 5pm, you had to be around the GA line for most of the day. That part was actually a lot of fun, as you would get to know the people around you in all. To me that was totally part of the GA experience, it makes the show even better in the end. Then at around 4pm, people would start getting more serious, bring their extra stuff back to their car, and then actually stand in line in order four 2-3 more hours. Those were the longest, I can tell you.
I hope things go the same way this time around. I can't wait!