I ran the Bolder Boulder 10k Monday. There were supposedly more than 53,000 people. There were dozens of starting waves a new one started every one or two minutes. I was in the first wave behind all of the wheelchairs. It was all of the best runners that were not in the professional race. That being said the top men and women in the non-professional race were running as fast as some of the people in the professional race.
I had never run in a race with more than 10,000 people and let me tell you it is a different experience. In most races there are a few hundred people and where I run in the pack it separates out so that near the end I am more or less running alone. Several times I have gotten near the end of the race and seen the nearest person ahead of me 20 or 70 seconds ahead and looked back and seen no one as far as the next curve (20+ seconds). Monday was different. Four of us rounded the last corner together only seconds behind another half dozen people. It was a constant parade of people. After the race I sat in the bleachers and watched the people just stream across the finish line. If we say that people were finishing over a span of about four hours thats a little under four people per second crossing the finish line.
It was a nice experience. As far as I saw it was set up very well, but I am pretty low maintenance. It had that big city race kind of feel where everything costs a lot of money. Of course they had lots of coupons and free stuff to go with the entry fee unlike smaller races. Road running is a pretty fun sport. Everything from odd distance, free entry, time yourself races to three digit race fees that include jackets, free food, tens of thousands of people, finishing medals, and prize money big enough to retire to an inexpensive country at the age of 27.