You can go straight to http://ipv6.google.com/
, but that doesn't get you anywhere near everything over IPv6.
From a practical standpoint, Linode doesn't meet at least two of the requirements:
(1) Separate DNS servers for your IPv6 users (not shared with IPv4-only users)
(2) Users who have opted in to IPv6 services and know how to opt out if they experience problems with Google services
The opt-in requirement is a bit of a laugh nowadays, for sure. I should have snuck that into our wedding vows. Alas, it was hard enough yelling the part about there being no warranty either expressed nor implied.
Warning (10631): VHDL Process Statement warning at signature.vhd(1): inferring latch(es) for signal or variable "disclaimer", which holds its previous value in one or more paths through the process