It looks like MacOS 10.7 (Lion) has fully functioning DHCPv6. It’s about time.
Before:
After:
pfSense setup:
Using Internet Systems Consortium DHCP Server 4.2.1-P1 as the server (on my pfSense box) I am able to get not only a privacy address (via stateless autoconfigure) but also a normal EUI-64 address as well as an IPv6 address via dhcpv6.