Exodus of Ysondre-US has just scored the world first 25-man Yogg-Saron with 0 Keepers, a.k.a. Heroic: Alone in the Darkness. A quick look at their site proves it to be true, complete with screenshots.
This achievement, when Ulduar was first launched, was largely considered to be mathematically impossible. One or two nerfs to Yogg-Saron more or less proved that to be true. The recent nerf to the spawnrate of the Guardians of Yogg-Saron wasn't aimed at the encounter with 4 Keepers up. It was aimed at the encounter with few (or zero) Keepers up. Without the buffs those Keepers provide, the encounter gets more and more difficult. As someone who has only killed Yogg-Saron with all 4 Keepers in the last few weeks, I fear seeing the fight with zero. Major, major props to Exodus.
They were rewarded for their efforts with