I know this post is a little old now, but it has been a great comfort to me and only now can I manage to comment - yes, the worst part is saying goodbye, which we had to do 2 weeks ago. She was only 9, seemed to be in amazing health and had more energy and stamina than ever before. Then with no warning, a hermangioscarcoma tumor burst on her spleen. Sometimes if it's just the spleen that's affected, it's ok, but she had them on her liver too. In the course of 6 hours, we had a dog we thought would live at least another 5 years to no dog at all :( It's indescribable how sad we are about this and I worry and wonder when we'll feel better and when we'll ever feel ready for another dog without comparing it to her. Thanks to everyone else for sharing your stories, I'm so sorry for all of your losses.
Besides this worst of the worst part, the second worst was that she was 7 when we had a baby, and she didn't like the baby. She bit him once when he was starting to crawl, a graze on the face. I thought my husband was ready to say goodbye then. I was so scared if it would happen again so we decided we had to keep them in separate rooms at all times, or make sure one of them was thoroughly supervised if they were in the same room. That was extremely annoying and difficult, and also kind of heartbreaking because I was really hoping for one of those story book "my dog would do anything for my baby" type things.
That's the only thing I haven't seen anyone else mention. But we dealt with monthly doggy vomit for no reason, she ate anything in sight (and we had to make her puke if it involved raisins or chocolate, which it often did) so we had to always keep food off of ANY reachable surfaces and constantly warn guests to do the same. She also shed year round. We both worked full-time out of the home for 3 years of her life and started her in doggy daycare once a week for $25 a pop, which made her sooo happy. She had two serious health concerns in her 2nd year that resulted in one surgery, lifetime prescription diet and medicine, and annual checkups with a dog cardiologist. Her annual cost in the last few years averaged $2000. But we didn't blink at paying for any of it, or paying $2000 for "just in case" surgery at the end vs. immediate euthanization. Of course this is because I try to be Mustachian and we had the funds. I don't know how anyone who doesn't have significant control over their finances manages the financial ups and downs of pet ownership (credit cards I guess).
I really loved the reliable schedule of walking and feeding her twice daily, and am 75% homebody so I didn't mind having her as an excuse instead of going out and spending money. She almost NEVER barked or growled (this is my main worry with a new dog), and was housetrained upon adoption (a rarity), and she had a perpetual puppy look to her. She really was the best dog for us and we were starting to successfully train our son to be more gentle and and understanding with her. He is still asking for her and I can barely handle answering him.