I have never had a dog that smiled, but I have seen other people's dog smiling, and I think that it is totally awesome when they do this.
Shopgirl, I can just imagine your little Yorkie smiling at you ! Chipper, my Yorkiepoo, does have his little things that he does. When we are going to eat something that he wants bites of, and he is trying to get our attention, he will sit I and then kind of "squeaky-talk " to be sure we know that he is there and wants a bite.
If we still don't feed him, then he goes into his "praying routine", where he puts his paws along side of his nose with his head tipped down , for all the world as if he were saying grace for his meal.
After that show of attention, we always have to at least give him his little taste.