I also see that the "sweeper" panic I remember feeling last year is alive and well here too. I can tell you a few things about the sweepers. I saw them at the end of the magic kingdom after I waited in line for EVERY PHOTO in the park. I was standing in an incredibly long line for Sleeping Beauty and they went by and shouted to us that we would have to catch up to them, and don't hang around too long. Of course we panicked and I wound up with a photo with a bunch of strangers because we wanted to get OUTTA THERE.
So I spent the next few minutes catching up to them, and then the next mile or two trying to leave them behind, though I did stop for more photos, so I'd lose them, stop, then see the balloons coming up, then push it, then another photo...eek balloons!...hustle...etc.
They weren't predatory like people imagine. Quite the opposite, in fact. I have to wonder if they're not licensed social workers based on some of the stuff I have read about people who got swept. What I saw when I passed them was a BIG group of women running with them, encouraging each other, getting encouragement from the balloon ladies. It was like a pace group, but it was a moving support group. I don't know how many of those women wound up crossing the finish line, but what I saw (briefly--I wanted OUTTA THERE and had legs that could do it that day) was a supportive group of people who were getting each other through.
There was a chilling moment just past mile 10. You go up a long cloverleaf type highway on-ramp, which then bridges the highway you just came from. I started that ramp with a huge crowd of runners, and the balloons well behind me. Once I got to the overpass, there was NOBODY on the road beneath me. I think the 10 mile marker is a key point for the sweepers. I saw no indication of sweepers after mile 10, and I did see people bonking at that point. I suppose you could drop out past that point, but everything I've read and my own experience seem both support the conventional wisdom that after that overpass, nobody's taking you off that course unless you sit down or start running backwards.
So that's what I have to say about the sweepers. Happy to answer questions.
Cate
PS/ETA: I should add that my clock time was 4:09 (chip time 3:43, corral E out of H), so I think that 10 mile sweep was for those who truly weren't keeping up a 16MM....AND started in corral H OR were way below 16MM. See my other post regarding corral placement, but I'm guessing if you register early and are truly trained for a 16MM, you won't see those sweepers. Unless you're a dope and stop for every photo like I did.

But I knew I could outrun them in a pinch, and so I did!