Thank you for pointing this out. It happened to me, and I was kinda hoping it was a problem with my side. However if it's affecting others, it must be a result of my recently moving the forum CSS (style scripts) to the filesystem rather than the database. Clearly it didn't have the desired effect (taking load off the database) and only threw up a new problem.
CSS has been reverted to the database.
Those Service Unavailable pages were a result of setting the server to limit the site to 2000 connections. For whatever reason, this just made everything worse, so I've disabled that too.
:constipation: *sigh*