Greyhounds can make great pets, just be careful with two things:
1) most don't know how to go use stairs (at least those that race on the east coast). I worked at a vet that helped out after a CT track closed, and we got about 6 spays and neuters a week throughout the entire summer, and while awesome dogs, none of them knew how to use the stairs. So if you are planning on getting one, you may want to make sure you live in a house or on a lower floor, or get one thats already learned how. They do learn how to use the stairs of course, but there is a learning curve (going up is easier for them to learn than going down).
2) Many cannot be trusted with cats because they were taught to chase small moving objects. Some are advertised as "cat-friendly", but while working at the vets, we had 3 or 4 cat friendly dogs kill the family cats. We also had some that were great with cats, so while its not guaranteed there will be a problem, its definitely something to be aware of.
That being said, its amazing how sweet the dogs were. The ones we saw would come in with whip marks and cigarette burns, some worse than others, yet they would wag their tails and let us do anything to them. Where I work now we have a few clients with retired greyhounds and they make great companions and love to laze around all day.