Tim Simpson had two very witty pieces at the RCA Summer show:

Natural Deselection is an instrument that empowers plants to control the fate of others using sensors and mechanised shrears in a Darwinian “race” for survival. Sensors set above three plants detect the first to grow to a specified height, at which point it is saved and the others chopped. According to the designer, the installation engages the viewers in suspenseful anticipation. As the race unfolds, the viewer is held between the slow, intangible pace of the plant’s growth, and the swift wiolent climax waiting to occur.

Another of his works is Subversive Sightseeing, a coin operated public telescope that digitally superimposes epic fictions onto the London landscape. Installed on Hungerford Bridge, it is intended to recognise the cinematic ingeniosity of our fantasies and the ramifications events such as 9/11 have on our collective imaginations.

A video to give you an idea.
Also digged by Tom Coates.