For those interested in solving this problem...
Cats generally use furniture because it works better than the alternatives they are provided. Companies aren't selling your cat a scratching post - they're selling YOU the scratching post.
If your cat uses a particular piece of furniture, find a post of similar size/shape and place it next to it. IE, if they're scratching the back corner of the couch, get a 3 foot tall post and place it next to the corner of the couch. If they're tearing up the rug, get one of the scratchers they stand on, and place it near that spot.
Cats scratch in different ways/angles/shapes to not only sooth their nails, but also to stretch certain muscles. If you can give them a scratcher that is aimed at similar muscles, it'll be more pleasant to use than the furniture, and they'll likely use that instead.