Just wanted to drop a note as a was pretty harsh on Apple when rumors
of them not including DHCPv6 client support were floating about. In
the past few days I've also seen people post that OS X doesn't have
DHCPv6, because they were looking for "DHCPv6" in the UI. Thankfully
these reports are false.
Just tried it myself on a newly upgraded Mac.
Quick testing shows that when "Automatic" is used for the IPv6
setting, OS X will correctly look at the A, M, and O flags of an IPv6
RA and make use of DHCPv6 when instructed to.
Thank you to everyone at Apple who made this happen. Especially James
Woodyatt, who I gave a piratically hard time to wearing my end-user
hat 
In a message written on Mon, Jul 25, 2011 at 10:50:21AM -0400, Ray Soucy wrote:
Just wanted to drop a note as a was pretty harsh on Apple when rumors
of them not including DHCPv6 client support were floating about. In
the past few days I've also seen people post that OS X doesn't have
DHCPv6, because they were looking for "DHCPv6" in the UI. Thankfully
these reports are false.
Just tried it myself on a newly upgraded Mac.
Quick testing shows that when "Automatic" is used for the IPv6
setting, OS X will correctly look at the A, M, and O flags of an IPv6
RA and make use of DHCPv6 when instructed to.
Thank you to everyone at Apple who made this happen. Especially James
Woodyatt, who I gave a piratically hard time to wearing my end-user
hat 
I can also confirm, and even to the point where you can disable
IPv4 and have a working IPv6 only client. It does DHCPv6 to get
namesevers and the like, Safari works just fine for browsing IPv6
only sites, and there seem to be no hangups.
Several other message boards point to a lot of changes under the
hood in the Objective-C sockets classes to implement "happy eyeballs".
That is if a host is dual stacked and has both A and AAAA it tries
both and caches which was faster and uses that for future connections.
I'm unsure right now if it is just connect times, throughput, RTT,
or what other metrics might be used, but apparently the result is,
well, happy eyeballs.
+1
Running successfully on Lion with DHCPv6-supplied resolvers at the IETF meeting this week.
Tim