I feel your pain, HD. Just a couple months ago we had to put down our dog of 14 years down. I have tried to avoid this thread but seeing the picture of your pup got me.
Brooke was the best dog I could have ever wanted. So sweet, never acted out. Little kids could climb all over her and she never cared. I hope one day I have a dog with her same temperament. It's funny, the reason we got her was because we heard about a farmer who's dog had some puppies and he was stuck with this last one that he couldn't get rid of. Every time people came to look at the puppies she ran away and hid. All she cost us was a bottle of whiskey.
Her heart and lungs and vision and everything was strong right to the end. It was arthritis that got her. It eventually got to the point where she couldn't get up by herself and could barely walk. It was heart wrenching to see. She was still trying to be happy but we knew it was time. Hardest thing I have had to do in my life.
Edit: can't get picture to work....here's the link.
http://img831.imageshack.us/i/img0063hv.jpg/