Lots of commments on military applications, but bipedal robots are inferior to wheel vehicles, planes, and aerial drones, in terms of speed and maneuverability.
Everyone's so afraid of Terminators hunting them down, when in reality, mostly invisible , and mostly silent, Predator drones from a mile away that will kill you with precisely targeted missiles should be your real fear. Or commercial quad-copters carrying anti-personnel mines.
The expense, complexity, power, etc to build bipedal assassins is higher than wheeled RC vehicles, quad copters, and missiles.
The weapons that exist today are much more scary than these robots.