They asked during registration what pace you ride, which worked out fairly well. After the first session they made a couple adjustments, but they were 80% of the way there from the start. You could quickly tell who had more experience so the grouping worked out well. Nelson is pretty tight though for groups to pass other groups, so there were some hold ups. Trying to catch Andrew Nelson out there was a lot of fun, unreal how late he brakes.
That's the first I've heard of such groups. The last time I did FAST was 2003 I think. They used to divide into groups throughout the day based on lap times. That way the riders would stay closer together in the groups on-track and benefit more from the on-track instruction.