I recently ran into the need to parent several layer to a null in an other, higher level composition.
Sadly the parent link doesn't work across different comps!
I hat to link the values for position, rotation and scale by hand for each layer, which was quite annoying.
I'd like to the the possibility to parent across compositions!
Thanks a lot!
Did you use the Copy With Property Links command?
I wasn't aware of this feature.
I tried to parent the layers using the lasso next to the parent option, which didn't work.
You can use the expression pick whip to go between compositions when writing expressions, but not parenting. However, the new feature that Todd mentions is even easier.