All I can say is obedience training is a must. (but that's true for all dogs).
My dad has a teacup yorkie named Boone, and it's been quoted accurately that they're little dogs with huge personalities. This little mess is a terror, but again like I said he has had no discipline or training.
On the other hand my sister has a standard sized yorkie and he is the best dog ever. He is about 10 years old now, and unfortunately starting to get cataracts, but is a wonderful dog. You can have a house full of guests and he just sits on the couch and lets whoever wants to pet and love him. Great dog!