I rushed yesterday (Wednesday, a two-show day right before Thanksgiving) and arrived right around 8am. There were 12 people in front of me, but I didn't think to ask how early the first person got there. By the time the box office opened, there were at least 40 people in line, possibly more. I didn't stick around to see how many people got tickets but I can't imagine everyone did.
There was talk in line that they tend to give out 20 tickets, but I'm not sure if that's a hard and fast rule or if it's subject to availability. I was ticket number 16 or so for the matinee. I just needed a single ticket and got orchestra row Q house right, which was a perfect view. I saw the woman who was next to me in the rush line after the show, and she'd gotten a partial view seat further up in the orchestra, and she said she had a lot of trouble seeing, just as a warning!