The only thing in my interfaces file is:
iface lo inet loopback
My wireless is currently turned off via the switch on the front of the Serval and I am plugged in via the Ethernet cable. I actually experienced an insanely slow startup or complete hang up (not sure, blank screen and I powered it down) when I had the Ethernet cable plugged in while booting. Not sure what to do...
No worries though, I use the Network Manager icon up by the clock exclusively.