[justeleblanc]

   $ ip addr show eth0
   2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
      link/ether 00:15:5d:23:d8:89 brd ff:ff:ff:ff:ff:ff
      inet 172.27.50.201/20 brd 172.27.63.255 scope global eth0
         valid_lft forever preferred_lft forever
      inet6 fe80::215:5dff:fe23:d889/64 scope link
         valid_lft forever preferred_lft forever
   $ ls /dev/eth0
   ls: cannot access '/dev/eth0': No such file or directory

And besides, what would it even mean for eth0 to "be" a file? What happens when you try to read it, what happens when you write to it?

[stonogo]

In Inferno (and Plan 9) it appears that network devices are filesystems -- e.g. there's a /net/ether0 directory which contains files with access semantics corresponding to various configuration and throughput tasks. I've read that it's even possible to 'mount' a remote network device on top of a local one, effectively tunneling traffic through the remote system. It's an interesting concept but I'm not sure of its utility, having never really used it.