I think that a lot of it is conditioning. Those of us who have always left our dog alone for 4-5 hours at a time, have dogs who are used to that. Honestly on days when I am home all day, Syd gets cranky in the afternoon because she hasn't had enough nap time.
Any puppy...but specifically a toy dog...is a life change. But if you are willing to accomodate the needs of your dog by doing things like coming home on your lunch break...I think that you will have a happy and well-adjusted dog. Do you spend most of your leisure time at home? I would be more concerned with a prospective owner who works 8 hours a day and then goes out on the town every night. If a good majority of your non-working hours will be spent at home...then you should be fine. If I can work 60 hours a week and still own a healthy yorkie...then so can you!
