Now, I can already anticipate the comments pointing out that this isn't a World First, because an Asian guild already killed Garrosh in 10-man over the weekend. Since Blizzard made several key changes, alas, Asian guilds can't really be considered as participating in the same race as the Western servers. For starters, they have separate 10- and 25-man lockouts, allowing two runs per week and better gear. They also have significantly higher item level drops in 25-man. Boss health is increased to reflect that, but only in 25-man, not in 10-man. So it's not the fault of the Asian servers, and you might wish to assert that regardless of the substantial gear differences, a world first is a world first, but Blizzard removed Asian guilds from the NA-EU race by making these changes. If you want more information, Manaflask has a great article.
Now the race is on for the bronze and silver medals, and excitingly, US guild Midwinter is representing the Alliance in the top five. It'll be really interesting to see whether an Alliance guild can take one of the podium positions. WoW Insider congratulates Method on their World First!