The new u-boot code now calculates a unique ID for the gumstix, based
off a read-only serial number in flash. This number is stored in the
read-only "serial#" env var in u-boot, and is passed to the linux
kernel where it becomes the serial number displayed at the bottom of
/proc/cpuinfo. The serial number will also be used to calculate a
usbnet MAC address for your gumstix, ensuring that it gets the same MAC
address on every boot.
Currently, the MAC address your gumstix gets has a slight chance of
conflicting with the MAC address of another device out there somewhere
in the universe; we will be obtaining a MAC prefix from IEEE, and
updating the MAC calculation code to use that prefix in the future, but
for now, be aware of the possibility of a MAC collision.
The reasoning behind having a gumstix serial number available to
software is that it will allow more easy tracking of which gumstix is
which in potentially *large* deployments of gumstix, where you might
have thousands or hundreds of thousands of them scattered through a
deployment, and you need to know which is which.