A great rotating paceline will alternate its rotation based on the wind, so the guys pulling off are blocking the wind for the guys moving forward.

That said, what is often lost about pacelines is that weak riders still help the group. If everyone is taking a 30-sec to one-min. pull and you can only give 5 seconds, you still help the group by providing a body for riders to hide behind in the group. So, keep that in mind.

That pace line is machine. They blow by that group ride.
Impressive

What? What people? Oh, you mean the other two guys in your group of three. How considerate of you.

Really does depend (on a number of factors not just individual strength). My preference is definitely a constant rotation so usually sub30 sec pulls. Everyone stays fresh and active like a swarm hellbent on the group goal. The reality is most groups are not evenly distributed in terms of strength/conditioning so something approximating a constant rotation develops with stronger riders taking a longer pull to help the group more. How big a difference is the "depends." The other big factor is knowing and trusting the other riders well enough to keep tight, even and consistent with the line and the traded pulls. Easy for teams but much more difficult for most of us schmoes who ride with ever changing groups...

LOL. One does what one can do for the lesser among us... (big tongue in cheek for those who don't speak sarcasm)

Like it has been said, it depends on too many things: wind speed, terrain, length of the ride, speed of the ride overall, purpose of the ride overall, composition of the group riding, etc. Typically, I would say the faster and the bigger the group, the shorter the pull should be and vice versa. I also go by time and not distance as time is constant regardless of terrain or wind while the over isn't. I will admit it does irritate the hell out of me people that do sit on the back of a group and just let a small group at the front do all the pulling. It is one thing not to be strong enough to do your equal share of the pulling (I can relate to that most times), but it is another just opening a hole in the group for other riders to come in, which int arms makes a yo-yo effect on the group behind those pulling. If they just rotated to the front and came off after 20 sec (enough to allow the rider that just got off the front to move back far enough), it would still provide quite a bit of a break for those pulling allowing them to pull longer and even faster.

Cool video. Would I be correct in assuming the car that shows up a couple times but never passes is some sort of escort to keep them from being run over? If there isn't a posted minimum speed, is that legal? Also, is there a reason they seem to be rotating counter-clockwise? For some reason it seems groups usually go clockwise (i.e. pull on the left and dropping off to the right)? Wind?

Yes wind. You want the decelerating side getting the wind, thus protecting the faster side of the rotation.

Different group rides have different characteristics and sometimes they even vary depending upon who shows up from week to week.

Some group rides are hard, competitive race-simulation workouts. All bets are off there. Sometimes you'll have half the riders struggling and not taking any pulls while the other half is trading attacks at the front.

Some group rides are much more of a cooperative effort and have structured rotating pacelines.

Some group rides are more social. These may have a double paceline with riders pulling up to their comfort level and dropping back in pairs.

Random charity ride pacelines may just have a handful of strong riders pulling a very long train. Be careful grabbing the back of these. The accordian action can get sketchy.