We actually have a PTer (who is not currently active) that has a deaf Australian Shepherd, Miko. I met up with her at the park a couple years ago and you'd never realize he was deaf unless you paid attention to the fact that Di never called out to him. He'd run off to play as we walked around the park, but he always looked back to her for a signal.
Also, my niece has taught her dog, Lucy, several hand signals she learned from a deaf person a couple years ago. I guess you could say Lucy is tri-lingual. She knows English, Spanish and Sign Language.

I think it is a great thing. We have a dog at the shelter right now that is "hearing impaired" (that's what they listed her as) and my niece wanted her. LOL