We have a lot of Greys in our classes and they're beautiful but very hard for their owners to reach, they're race rescues usually though if that makes a difference.
I actually have a lot less experience with track dogs. Most of the Greys I have been around are AKC or import lines, bred for show and/or lure coursing. I would think though that the way dogs are raised for racing would affect how easy they are to train. I am not someone who thinks all or even most racing Greys are poorly treated but from day one, they are raised to make them into great racing dogs. That doesn't include teaching them that learning is fun and doing stuff with people is fun. IME many people who adopt Greys are pet people with low expectations of the dog and limited training experience. Which is fine but it's certainly not an ideal situation to see what the dog would be capable of training wise.
Still the Never Say Never Greys are really nice agility dogs and all have been retired racers:
http://www.youtube.com/watch?v=gZ4SG8Wi3bQ&feature=share&list=UUE61xyPi2XqUaNhBLIge9WQ
Of course, she does pick her dogs carefully. Her newest is a pup from a breeder and she has lots of very adorable videos of her on Youtube too.
Patricia Gail Burnham has been pretty successful in conformation, field and obedience with her Suntiger Greyhounds for many, many years. She wrote what might have been the first positive training for competition obedience book there was.
The one I raised, by 8 months knew so many behaviors and was so joyful about doing stuff. She was really smart, cute, good at shaping and just a really enjoyable dog to work with. She was into tugging and of course chasing too. She was clicker trained from a young puppy on and I think that makes a huge difference too. Sighthounds really don't seem to understand their owners using aversive on them to get them to do something. I think because they were not bred to work with humans in the way herding or sporting breeds were. Using correction with them just makes them...sad. I'm not saying people don't successfully train them using correction based methods, just that they generally are pretty sullen.