Has anyone used this particular prescription diet and if so, what did you think of it? Any issues? Thanks for any input.

That's the joint health one, right. I know someone who knows someone that has a dog on it that lost alot of weight on the food and is going quite well with it's arthritis and mobility.

However, honestly, I would't put some of those ingredients into MY dog:
Ground Whole Grain Corn, Chicken By-Product Meal, Flaxseed, Soybean Mill Run, Brewers Rice, Soybean Meal, Peanut Hulls, Chicken Liver Flavor, Fish Oil, Pork Fat, Dried Egg Product

My 11 year old girl is on it. She looks great (fit) and gets around WONDERFULLY! She had stopped jumping up into the car, but now does so without any problems. She runs and plays with all the other dogs with gusto. She has been on j/d for a year and I saw huge results before 6 months.
My friends who have known this dog for a long time have been very impressed with how fit she has become.
(She had always tended to carry alot of weight.)

Just wanted to add that I had never fed any Science Diet products before. We always jokingly referred to them as "Science Fiction" products. We had a research veterinarian come to speak to all the local vets/techs about osteoarthritic pain management in canines and he recommended this food in conjunction with Rimadyl or Deramaxx stating that once the dog has been on the regimen for awhile, you should be able to wean them off the NSAID.(And he was a pharmaceutical rep, not a dog food rep.)
He made a believer out of me.

I was very sceptical when my best friend decided to put her 12 year old bitch on this food.... it WORKS!!! As the breeder of the bitch in question, I had nothing good to say about SD foods and much preferred the idea of supplementing her normal kibble.

Well, from a lethargic oldie lacking in gusto and unable to jump into the car, a month down the road she was taking long walks, bouncing around and simply unrecognisable. Maybe some of our preconceived ideas about what dogs should not eat need to be reviewed...

Thanks for the encouraging replies. I have an 8 year old boy with a bad elbow and he walks like an old man. I've tried him on several meds, including an NSAID, and they are not helping. My vet has now recommended adding the j/d diet to his current med regimen. Your results sound promising. I will try it. Thanks again.