David Goldfarb was the lead designer of Battlefield 3 until today. Kotaku reported that Goldfarb left Digital Illusions Creative Entertainment to pursue other things:
It was time to move on for me. Fans have nothing to worry about.
Short and succinct. EA has not made a statement regarding the departure, but we will update when they do. This action is slightly confusing given the long-term nature of Battlefield 3's life on consoles and PC. The Battlefield Premium service just launched and many DLC packs are still ahead of the game.
We'll update as more information becomes available.