Ensidia, the European super-guild that resulted from the merger of SK-Gaming and Nihilum last year, has just made the world first kill of the 10-man version of Algalon, Ulduar's true final boss. Algalon is only accessible after completing every other hard mode in Ulduar, and guilds are only given 60 minutes per week of attempts on him. 25-man Algalon has not yet been killed.
For details on the loot, see Ensidia's announcement; there's some great stuff there. Mek, from Ensidia, had this to say about the fight: "It's a pretty intense fight but not quite as hard as Blizzard made it out to be. The 1 hour timer is the real challenge since you must do a perfect attempt within it." Of course, I think "not quite as hard" for Ensidia is probably a pretty good challenge for the rest of us mortals. Congratulations, Ensidia!