I have two yorkies, both very small. My boy is 2 years old and weighs 4 pounds with a full belly!

He varies between 3 pounds 14 ounces to 4 pounds. My girl is 4 months old and weighs 1 pound 11 ounces. I have never had any health problems with either of them, no broken bones, and no hypoglycemic attacks. Both of mine sleep through the night without having to be up and fed every few hours and we go for walks outside in the colder weather and they will run around and play like they are "big dogs"

I think you'll find there are just as many health problems in larger yorkies as there are in the tiny ones. I think what is most important is not size, but the bloodlines your pup comes from and how many "clean" generations of no genetic health problems they have. Both of mine are AKC and have incredible champion bloodlines and I believe that is why they are as healthy as they are. My boy was bred to be a show dog and has 67 champions in his bloodlines. I think the only thing you have to watch out for with tiny ones is you have to learn to be aware of them. Watch where you step, watch where you leave things. My girl is a jumper and will jump on anything and jump off anything so I have to be careful with her. If you have larger dogs or children that is something to keep in mind as well. As for me, they are my only pets and I have no kids so having tiny ones works great for me!