The main trouble is not being able to see the tracers...as a noob driving a panzer (and I'm still a noob) I got nailed repeatedly by someone on a flak gun. Not being able to see the tracer, I had no idea where the shots were coming from and didn't realise for a few deaths and after having it explained to me that it was probably manned acks, I assumed there was a tank somewhere that I just couldn't see.
If you can see ack tracers from planes, why can't you see them from GV's?