I noticed at the office today that some IPv6 clients were unable to access the site, getting the helpful message "Database Error". The problem is that IPv6 addresses in human-readable form can be up to 39 characters long, but SMF logs all requests in a table with the IP address encoded into a column limited to 32 characters in length. If you are on IPv6 and your address happens to be longer than that, you can't use the forum. Like, at all.
I've redefined that column to have a length limit of 100 characters, which should be enough for anyone, and confirmed that it Works For Me now. Let me know if you notice any more issues on IPv6 clients (although, if you do, you likely won't be able to post in this thread...).
IPv6 still won't work perfectly. Your IP address will be logged as 0.0.0.0, for instance, because SMF can't handle the fact that this isn't 1995. But you should at least be able to browse and post with IPv6 now.