Hi, one thing:
"net.ipv6.conf.default.use_tempaddr = 2" breaks TCP sessions.
I've been using IPv6 for some time now with this turned on and nearly all worked BUT: ssh sessions hung after some time. I first expected some sort of ssh bug since everything else worked but I wiresharked it and the issue is that privacy extensions rob the active IPv6 and assign a new one which breaks the TCP connection, of course.
This can also be found here:
The report is from kernel 2.6.17 and still valid as I'm currently running
2.6.38-8-generic #42-Ubuntu SMP Mon Apr 11 03:31:24 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux
could'nt find a bug report regarding that but will search further or create one.