According to RadioLab’s podcast on speed, light can be slowed down to travel at just 15 miles per hour or halted entirely in a cloud of very cold sodium. Also, the nervous system in the human body sends signals at 60 miles per hour, which seems a bit slow until you consider that the signals don’t have to travel very far. Also, one linear foot of computer cable slows a signal down by one nano second–this apparently matters a great deal in high frequency trading, which now makes up 60% of the stocks traded in the New York Stock Exchange.
http://www.radiolab.org/2013/feb/05/
