[ebs]

If you are seriously playing with internal Kindle software (e.g. mucking with java stuff), I recommend making usbnetworking "auto-startable". Otherwise, if you corrupt something in framework, you'd need serial console for recovery.
Add this simple script to /etc/init.d:

[root@kindle init.d]# cat /etc/init.d/usbnet
#!/bin/sh

_FUNCTIONS=/etc/rc.d/functions
[ -f ${_FUNCTIONS} ] && . ${_FUNCTIONS}

US_ENABLE=/mnt/us/usbnet/AUTO

case "$1" in

        start)
                if [ -f ${US_ENABLE} ]; then
                        /mnt/us/usbnet/usbnetwork
                else
                        msg "not usbnet" I
                fi
        ;;

        stop)
                ;;
        *)
                msg "Usage: $0 {start|stop}" W >&2
                exit 1
                ;;
esac

exit 0

And then make it start-up script:

[root@kindle rcS.d]# ls -al /etc/rcS.d/*usbnet
lrwxrwxrwx    1 root     root           16 Jan  2  1970 /etc/rcS.d/S72usbnet -> ../init.d/usbnet

After that, you'll be able to enable usbnetworking automatically by creating file "AUTO" in "usbnet" directory on user partition