I have two cavaliers. Cedar is just shy of 12 lbs, and Willow just weighed in at 10.4lbs on Monday. While Cedar came from a breeder, she was not a good one. Willow is a rescue from a puppy mill. Both dogs are one year old.
While I fully anticipate health problems in the future (and perhaps not so distant future at that!), right now both dogs are healthy. Willow is being treated for excessive tearing at the moment, but otherwise she and Cedar have not had any significant problems. Neither is picky about food, either. They dive in when it is feeding time and they steal whatever the can.
While I do not at all suggest that breeding for "teacup" size is the way to go, I do not the little ones to be looked over due to a fear that they undoubtedly will be picky eaters or have frequent issues. Just like any dog, some can be picky, but others will not. Some will be healthier than others. Size should not be the only reason for selecting (or not selecting) a dog/puppy.
Cedar (tri), Willow (blen), & Holly (ruby)