OMG.How adorable.
Just a question.Do you have contracts made up for the new owners?What I mean is a spay/neuter contract....A contract stating that if for any reason they can't keep the pup,it's to be returned back to you?Have the new owners researched this breed?What health and genetic issues that this breed has?
This is something to definately think of if you haven't already. 
Yes, I do.
Perspective owners, if I don't know them personally, fill out a looong application, I do check all kind of references, and a contract is "a must".
As for genetic problems - it is a remarkably healthy breed, but just like any large dogs - HD could be a problem, sertain type of heart disorders and entropia.
New owners defenately doing a little bit of research on the breed (otherwise they wouldn't even know that dogs like that exist), they all ask a lot of questions (and if they don't - they don't get to have a pup) before and after they got a puppy.
LOL. It is not the ideal process, but we trying to improve it every time we go through.