Sunwell Plateau, the 25-player raid of which KJ is the last boss, was opened, but several "magical gates" were interposed between would-be KJ-killers and the demon himself. The last of these gates, giving access to KJ, was opened on May 20th/21st. SK Gaming got the world-first kill on him on the 24th, and Method and Nihilum quickly followed; and Deus Vox got the US first on the 27th, with Exodus following the day after (thanks, hyos). Nobody else has killed him, as far as I (and WowJutsu) know.
That may or may not be about to change, due to a new hotfix just implemented last night. According to Lead Encounter Designer Daelo, a change has been made to KJ's Soul Flay ability. It now uses "a much simpler rule" to determine its target: the target of Soul Flay is the player with highest threat against KJ (typically the main tank, I would think). Daelo notes that this is not intended to make the encounter easier nor mor difficult, but rather to produce "a more consistent, more understandable, and more enjoyable Kil'jaeden fight." Folks who have done this fight, do you think this is a good description of the change? Or is it a nerf, in the long tradition of nerfing raid bosses?