I use the ACC about 90% of the time on my commute to work. I'm in a manual so I can't comment on the start and stop.
I think it's excellent, takes some of the stress out of driving, particularly when it's bad visibility (fog etc).
I have experienced all of the above. On the rare occasion it does late break, it's a bit unnerving, but I manage to fight the instinct to break most of the time, but sometimes I have to intervene.
The space invaders are annoying, but not much you can do there.
When a car pulls back to the left lane, a dose of the right foot mitigates the delay on the ACC picking up the speed.
I find it's worst behaviour to be picking up a car that pulls in front from the left lane, in terms of it's reaction times. It won't register on the graphic there's a car in front until it's almost fully over, and it won't start to break until that point either. This is where I have to intervene most.