I think it has the potential to become very ugly, very quickly. It's similar to custody battles over children in a divorce. Not good for people or pets.

However, I think sometimes within a family, it works out well. My dad didn't want a dog, he thought he was "too old" to handle one full-time again. But he loved dogs, and missed having one. I took our newest dog, Karma, to his house every weekend so he could "dog-sit" the "grand-dog". He loved it, she loved it.