The Pong Clock from Buro Vormkrijgers plays games of Pong that last for exactly one minute each, with alternating sides winning. The clock in the middle keeps time/score.
Link (Buro Vormkrijgers site, 10MB Quicktime video)
(via Digg)
Update: Hijinx Comics sez, "It actually scores the time, with
the left side only scoring once per hour and the right scoring every
minute."