Never had a greyhound, but our neighbor has one she keeps, and supplements her pack by rotating through foster dogs one at a time. So, at any given time, she has Charlie alone or with a temporary buddy.
All of her fosters are track dogs, with varying degrees of familiarity with family life. They’ve all been gentle, careful giants, even-tempered and well-behaved. Some are skittish for a while; even Charlie sometimes moves behind his mom when strangers approach.
The cons as I understand them: greyhounds are physically sensitive. They’re bony and need to sleep on sufficient padding so they don’t get sore, and their skin is comparitively easily torn. They are gazehounds, bred to chase fleeing prey on sight, and not all of them adapt to living with other small animals – greyhounds are generally not killers, but they can go after cats, and of course rabbits and rodents aren’t safe around them. If they DO go for a small pet, they will be fast, of course. But that’s worst-case.
But the ones I’ve seen seem more like deer than dogs, pacing gracefully around the parking lot with our neighbor, stopping to politely touch noses with my friendly little pit bull, and then moving on. They do have a reputation for being relaxed and easygoing in the house.
I’ve seen a few at the dog park playing. It’s interesting that there’s sort of a hierarchy of speed among dog breeds.
There is a little white terrier of some sort who is quite fast despite his short legs. He plays with my pit bull Simone, who is faster than he is when she feels like running, but he’s a lot smarter than she is about the chase, and eludes her by cornering around obstacles. I thought Simone was fast until I saw the German Shorthair Pointers letting it all hang out. But they in turn were blown away by the Hungarian Vislas. Those dogs love to run – they come to the dog park and they just fly up and down the length of it, lean red rockets, and they go at it longer than other breeds.
And where does the greyhound rank in this tale? Sometimes it’s hard to say, because they often just watch the other dogs run as if it’s beneath them to actually do it themselves. Or maybe the dog park isn’t big enough for them to get up to full speed.
One day I saw a Visla running with a mixed pack of other dogs. He was just plain faster then all of them, and enjoying it, pulling away every time after they got close at the turn. He was just a streak as he galloped.
Then a greyhound took an interest in the chase, and pulled up beside the Visla. He was keeping up, but he wasn’t even galloping, just moving in a long, easy, ground-eating lope.
So I can’t tell you how fast greyhounds are from my dog-park experience, because I’ve never seen one have to go flat-out. Partial speed is enough for them to overtake everyone else. 
