That guy is me a lot of the time depending on the group, here in Seattle there are variety of group rides at various designated speeds and depending on who shows up and how many I might take 10-15 min pulls at the front right at threshold, to 1 min pulls at V02max, or no pulls and just try to hang on during the really fast rocket rides.
Since its not a race or formal training ride group pacelines can be flexible and dynamic. The main thing is that you are with like minded people if you're trying to cooperate ie don't up the tempo when you get to the front to try to show your strength and also get off the front before you start slowing the group down. The point is for everyone to work as hard as they can an still consistently recover in the pack/paceline to continue to work together to be faster overall