The server that hosts the forum, wiki and IRC was down for about six and a half hours, from about 17:00 to about 23:40 UTC, 2014-11-20. I'm still looking into the root cause, but the reason for the duration of the outage is that it happened in the middle of the night here, and I was asleep.
In response to this incident, I'm going to be looking into setting up proper monitoring soon. It's something I've been planning for a while and never got around to because the server has been very reliable until now. Hopefully this won't happen again, but I'd like to be prepared.