MinnMan

StanSeven has it right - maintain constant effort - at least for modest hills. That means slower on the climbs and faster on the descents.

On steep, very fast descents, the pace line will likely break up temporarily, as more space between bikes is needed to be safe. Similarly, on steep, very slow climbs, the pace line will break up as people have different climbing abilities. Regrouping at the top is normal.

Pulling a pace line well takes some experience. When the person in front of you moves over to end his or her turn and your turn begins, the first tendency may be to increase effort, but if you don't do that right, you end up opening up a gap behind you. It does take more effort to pull than to ride behind the puller, but gently increase your effort until you are going about the same speed as the previous pull. Then maintain.

Also, it's not always possible, but it's more polite to end your pull at the top of a climb than at its base.