For me, these symptoms started when i tried using Migration Assistant to move 450GB of data from my iMac - it never actually hung but would come up with "trying to reestablish network connection". After multiple attempts I ended up taking a Carbon Copy Cloner backup to a USB disk and restored from that.
It was only when I setup Time Machine to my NAS that I got the hangs, shortly after starting the backup.
Had multiple hangs till I found this thread and installed the E100 kext from MB 5.4.3.
So yes, you'll only get the hangs if you start pumping large volumes of traffic thru the NIC.