I've featured Boston Dynamics' BIG DOG robot on Free Planet before; looking at it you think, "Capable but ponderous robotic pack mule," fine for carrying equipment to/from soldiers in the field but nothing more.
You could mount a gun turret on it, but it'd be an easy target for any return fire.
CHEETAH, however, the latest superspeed robot from Boston Dynamics is another league of beast entirely, having a current top speed of close to 30 mph:
Can't work out why Boston Dynamics' latest sprinter can only run backwards (watch the treadmill direction) but you know what it made me think of?
TRANSFORMERS: revenge of the fallen's RAVAGE.