We are aware that our MySQL database servers are offline this morning (forum, review system, jargon buster etc.) and have begun an investigation of the problem. Hopefully it should be resolved shortly.

UPDATE 11:45am

We expect the database servers to be offline for another couple of hours since the problem appears to require some additional work, which is difficult on a Sunday. We aren't reliant on MySQL for everything so a large part of the site will still function without it.