I rebooted and my network is "down." eth0 is actually running, but
from what I can tell my applications like Evolution and Firefox are
trying to use lo.

I have the link set up

# cd /etc/init.d
# ln -s net.lo net.eth0

/etc/conf.d/net has config_eth0=( "dhcp" )

rc-update add net.eth0 default returns that eth0 is already default.
I can see it come up when I boot, but lo also comes up. I don't
remember ever creating lo.