Something to think about- if you have a grounf leakage in one piece of equipment, everything shuts down. How do you troubleshoot this down to the faulty item? Also, if your feeder is long, the (capacitive?) coupling to ground can trip the feeder breaker. I know the square D QO-GFI breakers list a max length for downstream conductors, can't remember what it is at the moment.
I asked a similiar question to an inspector once- If we have an area that needs a bunch of GFI's, like a commercial kitchen or similiar , can't we just put a Ground Fault system like those used for services on the feeder and hook it to a shunt trip breaker, and set it at 5mA??? He said that that would satisfy the NEC, but would be a really bad design, because of the reasons above.