A few things that I'd like to add:
The first is that I felt the Ghosts were underpowered, at least in the early game. It was useless against vehicles, useless against more than a couple infantry, and useless against air, so I never really built any after I had fully upgraded ones. The Banshee was the same way. I only ever built it to repel Hornets, but the Vampire was twice as effective, and so I never really tested out the Banshee later.
Also, the AI in Skirmish never attempt to contest Supply Poopers.
And, finally, unit intelligence pathfinding is pretty low. Units try to take the most direct route, and if it is blocked, don't look for other paths. Even if that other path is relatively short, they don't get it. Also, ordering units to go long distances may cause problems. I ordered a pair of Wraiths across the map, and while the path was pretty direct, they tried going in the opposite direction.
I like pi.