PXE Booting Raspberry Pis
ltm56.com
ltm56.com
I setup the boot order something like (sorry can't remember exactly) 1 - PXE, 2 - sd card, 3 - USB. That way I could link in the nfs boot directory and reboot each pi and have it come up on the netboot filesystem, dd a new image to usb or sd and reboot into a fresh new image.
I highly recommend the experience of trying out pxe boot along with your choice of automation.