Ifplugd

You can use ifplugd to automatically configure the ethernet port when it is plugged in/unplugged. I have ifplugd configured to automatically control both eth0 (ethernet) and eth1 (wireless):

 INTERFACES="eth0 eth1"

 AUTO="yes"
 BEEP="yes"
 IGNORE_FAIL="yes"
 IGNORE_FAIL_POSITIVE="no"
 IGNORE_RETVAL="yes"
 POLL_TIME="1"
 DELAY_UP="0"
 DELAY_DOWN="0"
 API_MODE="auto"
 SHUTDOWN="no"
 WAIT_ON_FORK="no"
 MONITOR="no"
 ARGS=""

 MONITOR_eth1="yes"
 DELAY_UP_eth1="5"
 DELAY_DOWN_eth1="5"

Also make sure that /etc/init.d/net.eth0 and /etc/init.d/net.eth1 are symbolic links to /etc/init.d/net.lo:

# cd /etc/init.d
# ls -l net.*
lrwxrwxrwx  1 root root     6 Jun  8 06:17 net.eth0 -> net.lo
lrwxrwxrwx  1 root root     6 Jun  8 06:18 net.eth1 -> net.lo
-rwxr-xr-x  1 root root 24402 Jun  7 21:22 net.lo

... and add ifplugd to your default runlevel:

# rc-update add ifplugd default