I just found this thread and read through it all rather quickly so I may have missed someone commenting on this. Folks that say they could have finished if they had been given a 'good' corral placement are incorrect.
People are placed into their corral based on estimated finish time. The individual runner/walker time doesn't start until their assigned corral goes over the mat. If you've trained to/race to the maximum pace allowed you will have enough time to finish the race without being swept.
People who move up in the corrals to get a 'good' placement end up causing more congestion and making the event more difficult for everyone.
I have one sweeping experience under my belt at Disney. A friend who hadn't run and was sort of Pooh sized was impressed with my running at Disney. She asked if we could plan on doing a Donald together. I said, "Sure, that would be great!"
We lived in different states at the time and kept in touch casually by email. She was supposed to be following a Galloway training program but was always rather vague about the status of her training when we talked. I figured she was a grown up and would stick to her commitments. I thought that until I met her at the airport.
I arrived first and got to her gate to meet her (we both flew SWA just different planes). My first impression was, 'There is NO way she has been getting any exercise." She seemed upbeat and I didn't want to hurt her feelings so I didn't say anything.
Morning of the race she's optimistic and happy so I figure we'll finish and she'll be proud to do her first half marathon and it will start a lifetime of Disney running like it did for me. We start the race with a nice slow 2 min run/1 min walk like her Galloway plan so I'm feeling happy.
We made it one mile before she said she had to slow down.

Our first mile took 14 min. We started to slow down from there.
I had never seen the sweeper guys on bikes before. They were circling like vultures by mile 5. They started threatening us by mile 8. I was trying to be supportive but I was getting a little angry at her because I no longer just suspected that she hadn't been training but now I KNEW. It ticked me off because my finishing record was being jeopardized and the only reason was that I had promised to finish with her.
Somewhere between mile 9-10 I realized that I would have been back at the room, showered and out to the parks if I had gone alone. I had been on the road for a longer time than any of my training runs and I REALLY had to use a port-a-pot. I made a fatal error and said I would run over and use one. SHE decided she should do the same thing. I told her to keep walking and I would catch up.
The only thing she did slower than walk was use a port-a-pot. I was done and standing outside the john waiting for her. What was she doing in there???
She comes out all smiles and starts walking. By this time we are passing the Contemporary and the guys on the bikes are literally screaming at us to pick up the pace. She doesn't seem to take them seriously or maybe she really couldn't walk any faster because she didn't.
We're with a clump of about 20 people. We're about to make the left onto the service road that heads towards MK. There's a little security shack there. I've run past it a million times. I had never noticed the big steel plates in the road before.
As we're making the turn a horde of race/security staff starts raising their hands in the air. waving them back and forth and yelling something. We're too far out to hear but apparently someone behind us understood because she took off running very fast straight toward the shack. There was a sudden metallic 'CLUNK' and two large steel plates spring up out of the ground blocking the road. Huh!
From our angle it looked like the force helped spring the runner up and over the plates allowing her to continue past the barrier and continue the race. The rest of us were stuck on the wrong side of the plates. Our little clump of 20 people grew in the hot sun with no shade or water to around 100 people.
My friend was chit-chatting with everyone and taking pictures.

I was stewing knowing we had been swept. We stood/sat/slumped there for about 30 min before they admitted they couldn't get a bus to us and we were going to have to do the walk of shame over to the MK to catch the monorail over to the finish line at Epcot. We ended up walking almost the whole distance of the half. They escorted us to a special tent and started handing out medals.

My co-racer (by this time I was sure she wasn't a friend) took the medal.

I refused but they literally shoved one into my hand. I ended up throwing it away.
That's my story. My friend ended up doing a Wine and Dine relay with her husband some years later. We don't have any contact now and I suspect some of it is based on this race. It felt like she had lied to me about something very important and I didn't really respect her for accepting that medal.
I think they should have an "I got swept" keychain and use the brooms from Fantasia.