Someone trolled the server with a massive amount of explosions that took out almost everyone's buildings, not exactly sure when though. I'm guessing one of the admins reverted it to repair the damage?
In other news, I'm using the GLSL Shaders Mod with Sphax PureBDCraft. It's flipping gorgeous. You'll need to tweak the config to get it running on your PC, but once you do, the dynamic shadows make the game so pretty it's nuts.