I think it kind of depends on the pup you would pick. Some yorkies have more 'problems' than others. I have heard of challenges with housebreaking, barking, health etc, but that really depends on the dog, not necessarily the breed. Trixie was housetrained within a week, hardly ever barks, and is extremely healthy. Also heard of possible problems with liver shunt, teeth (when they get older and you don't brush them regularly), knees.
What I have learned after three months is that yorkies are very loving. And to me, it is good practice for a baby
Trixie takes a lot of work. Because she is small, I have to constantly watch where she is going (so we don't step on her), needs to have a bath at least once a week, brushing and needs lots of attention.
Oh, one more thing... Don't expect to get a lapdog if you are getting a yorkie. They might like to lay on your lap for a little bit, but these little dogs are terriers at heart. They love to run, chase and run some more!!!