I think they are talking about the Cliff Race Pacers. I know I was trying to keep up with them when I did the marathon a bunch of years back. The problem for me was that they start in a specific corral and my corral was further back (meaning I would have to make up time to get to them). We saw them in our sights a few times but never quite made it to the group. I believe they are paced every 15 or 30 minutes and if you keep up with the pacer, you will make your race time goal (i.e. if you want to finish the half in 2:30 you follow that balloon throughout the race).