Not strictly Raspberry Pi, but I reckon it would be possible to reproduce with a Pi 2.
Here’s a lovely project from Jochen Alt. It is a robot lamp called Luci which uses an ATmega chip to generate PWM signals for the servo motors. The ATmega is itself controlled by an ODROID-U3 which does the facial recognition and computation of trajectories. The video is below. Head over to YouTube to leave Jochen some feedback!