We have a Doll Faced Silky Yorkie, and she's a wonderful dog. She's 6 years old and weighs about 6 pounds. She's not at all yippy. In fact, she doesn't bark at all unless she's outside and she sees some other animal.
Small dogs are VERY susceptible to tooth problems. In addition, they may have joint problems in their legs. Ours has luxated patellas, which is a problem with the knee caps. As the vet described it to us, the channels in the leg bone that hold the knee cap in place are so small, that they can't keep the knee cap in position and it starts to "float" over to one side or the other. Surgery is the only option.
Grooming doesn't necessarily have to be a problem. Yes, if you want to keep a Yorkie with the long hair style that you see in at the dog shows, it will be a major headache. But we keep ours in what's called a puppy cut. So even though she's a full grown adult dog, people think she's just a puppy. It's easy to take care of and looks great. I've attached a picture.
Yorkies are very intelligent dogs, and as someone else said, they're fearless. Ours backed a doberman into a corner at a pet store one day, but only because she wanted to play!