Never heard of any of them besides Facebook. Anyone famous?

Remedy and Funatics developed popular games. Though it's not said what they used "D" for.

Remedy is responsible for Alan Wake and Max Payne, Funatics for Cultures, Zanzarah, among others.

By following the links in the wiki:

Remedy: "integrating D with a typical C/C++ game engine as an extension language for use processing game logic"

Funatics: "D as a replacement for the parts of our infrastructure that use nodejs right now"

Pretty big names in their field.