Actually they are quite lazy. Mine gets all fired up about 8:00pm for 5 minutes. Wants to run around like a crazy dog then quickly tires. I guess it is like cheeta saving up the energy for the hunt. Most of the day he sleeps. He does love to go for walks....but not manditory.
The greyhounds that I have known have all been "40MPH couch potatoes", as was my Borzoi!