It was hotfixed and that should be showing up in our hotfix tracking blog tonight or tomorrow. http://us.battle.net/wow/en/blog/2259389#blog
Essentially it was being exploited to bring entire groups to the summoner, who would stealth past a few bosses, allowing the group to skip them. Guild perks should be just that, perks, and aren't intended to be game-changing mechanics. We would like to make it so that regardless of where the summoner is, the summonees are always summoned to the entrance of the dungeon, allowing this to still be very useful but avoiding that exploit-ability, but that will require further development.
We're also in the process of removing its use in Tol Barad while the battle is active.
Well, easy TB victories for us alliance on Dawnbringer will soon pass away. *sniffle*