I've only seen soft paws put on one dog, a young golden retriever. Actually, the largest ones we had didn't fit, and when the vet got to talking to the woman she said she took the pup for daily walks around the neighborhood and he said one or two times on concrete and they'd be worn through anyway. The best part of the story for me was her reason for wanting soft paws. She had wood floors and the dog was too playful and was scratching them. So we recommended baby gates to keep the dog out of these areas. Her response: The pup WAS confined with baby gates... but only TO the areas with wood floors so it wouldn't pee on her carpet!!
Guess you've got to pick your battles with some people.
I've heard leather really isn't too tempting for cats to scratch because its really smooth and their nails don't "catch" too easily on it. They'll go for carpet or other fabrics on furniture but most don't mess with leather. My cat was front paw declawed when I adopted him and he "scratches" our leather couch, but only to kinda stretch his legs, he'll do the corners of our walls too... which most cats don't do.
Soft paws can be very helpful in keeping from poking holes in the furniture just by jumping on or off it. Even mine has had a few problems with his back paws when he jumps around (when I forget to trim them anyway).
I've heard that its easy to train a cat for a scratching post, but have never done it myself. Basically, get them to scratch it by setting them in front of it and put their paws on, rub them over it like their scratching, etc. Also do it yourself so they SEE you "scratching" it and mimic your behavior (best to do without company, so you don't look completely crazy). Any time you see them start scratching anything you don't want them to, pick them up and bring them to the post. And give them lots of praise and treats when you see them using it.