Following are my notes as I enable IPv6 on my servers.
- The formatting of addresses changes. My lighttpd logs now start with addresses like ::ffff:1.2.3.3. That ::ffff: is IPv6 speak for "an ipv4 address". PHP5 also returns this new format when you as for $_SERVER['REMOTE_ADDR']. This has broken several bits of software that parsed addresses.
There will be more.