$ getent hosts mysql.com percona.com askmonty.org postgresql.org oracle.com sqlite.org code.openark.org skysql.com drizzle.org
156.151.63.6 mysql.com
74.121.199.234 percona.com
173.203.202.13 askmonty.org
2a02:16a8:dc51::50 postgresql.org
137.254.16.101 oracle.com
67.18.92.124 sqlite.org
69.89.31.240 code.openark.org
94.143.114.49 skysql.com
156.151.63.6 mysql.com
74.121.199.234 percona.com
173.203.202.13 askmonty.org
2a02:16a8:dc51::50 postgresql.org
137.254.16.101 oracle.com
67.18.92.124 sqlite.org
69.89.31.240 code.openark.org
94.143.114.49 skysql.com
173.203.110.72 drizzle.org
So only postgresql.org supports IPv6 right now. On the MySQL side Facebook is one of the known IPv6 users.
Are there any IPv6 database websites I forgot to include?
The World IPv6 Launch is June 6 2012, so there are still a few days left to enable IPv6!