Something I noticed:
If Medivacs are in the vicinity of Infantry that are attacking units/buildings, the Medivacs will hang around the infantry, and will ignore all commands except for a force move/right click. When the infantry finish attacking, if you didn't give the Medivacs any new commands, they will remember the last order you gave them and move to that position.
So, in combat, Medivacs will always be in position, even if you've got them in a control group with Marines and are giving force fire orders. I was hoping they'd implement something like this. Babysitting medics was one of my least favorite things about BW.

