Aaron Toponce over at Planet Ubuntu has an excellent article with graphics that really puts the vast size of the IPv6 address space in perspective in relationship to the almost used up IPv4 address space in perspective.
I would just add that 64bits of the 128bit IPv6 address space do not necessarily have to be dedicated to the MAC address of one’s Ethernet adapter. Google (IPv6-only link) does not do this on their servers and neither do we on our IPv6-enabled sites.
On a related note, the testing of OpenID login via IPv6 with Pay4Bugs as the OpenID IPv6-enabled rely party and IPv6-enabled OpenID provider that some kind souls on the The Great Pv6 Experiment mailing list had been helping with uncovered a least one bug in the Ubuntu 8.04 Ruby on Rails stack. We were able to fix the bug and a post will be coming soon regarding the details and the fix.