The DIY project Hope vs. Despair [bigspaceship.com] consists of an application that tracks tweets every 30 seconds, looking at the frequency of smiles and frowns, specifically :) vs. :(, and a physical device that displays the aggregate result.
The display device is basically a small rotating carousel within a larger stationary one, with a window cut out in the larger version, so one can see inside it. 10 slightly different iconographic faces ranging between the widest smile (Hope) and the saddest frown (Despair) are glued these onto the smaller carousel. A servo motor is mounted to the base of that carousel and connected the motor to a computer via USB. This allows the apparatus to react to a custom application, adjusting every 30 seconds to display the face that best conveyed the disposition on Twitter.
See also Weeping Willow.