If you look around theres actually stuff for that in existance now. The
current ex2fs keeps a UUID on each volume which is basically there for
just that reason (UUID's are statistically unique keys for objects - there's
an RFC for the UUID system too)
If you have an Ethernet card, (and the manufacturer of the Ethernet card
was competent about assigning Ethernet addresses --- some weren't,
unfortuantely), the guarantees on the uniqueness of UUID's is much more
than statistical, actually.
- Ted