This is a tough and touchy subject. First, I have never had one of my own cats declawed. However, I have performed the surgery numerous times.
What does the surgery actually entail?
The claws are removed by removing the last bone in the digit. Essentially, that would be like removing the ends of all your fingers. So, it is not just the nail itself that is removed. The bone has to be removed or the claw will re-grow. Not only will the claw re-grow, but it will re-grow in an abnormal way and cause a lot of discomfort for the cat.
How painful is the surgery?
This really depends on the age of the cat. Young kittens who are declawed before they are 6 months old usually recover within just a few days. After the first few days, they rarely show any signs of discomfort. Cats who are declawed over 6 months of age can act painful for a few weeks. So, if you are going to have the surgery done, the earlier the better.
What are some alternatives?
There are several behavioral modification techniques that you can try if your kitten/cat is destroying your furniture. First, cats do not like water or loud noises. So, if you spray them with water or blow an air horn every time you catch them scratching something they aren't supposed to scratch, this will be a major deterrent for them. They also tend to stay away from citrus smells. So, you can try using lemon or orange scents on the furniture you don't want them to scratch. Finally, they don't like the feel of plastic or aluminum foil on their paws. So, you can put a barrier they would have to walk across to get to their favorite scratching area. Next, you will need to give them an assortment of alternative places to scratch. These need to be more attractive than the furniture. Catnip works really well to attract cats to the post you want them to scratch.
Unlike most dogs, cats tend to take a toenail trim pretty well. I just get out a pair of regular fingernail clippers and use those to trim the cat's nails. Dog toenail trimmers are too big and bulky for the small cat claws. To trim a cat's nails, press on the end of the toe and the nail pops out. Then you can trim of the tips. By keeping the nails short, they will do much less damage when they do scratch.
Finally, they do make a product called "Soft Paws". These are guards that are glued onto the cat's claws. I have found these to be hard to use. They don't all pop off at once and so it seems to be a constant struggle to keep them on the cat.
I recommend trying all of the above alternatives before deciding to have you cat declawed. Especially, if the cat is an adult. However, I worked in an animal shelter for several years and one of the things that caused me the biggest heartache was to see really nice cats given up for adoption because they were destroying the furniture in the house. Many of these cats never got adopted. So, I would definitely support having your cat declawed, if the only other alternatives are to turn them out or have them euthanized. Most cats recover just fine from the surgery and go on to lead happy healthy lives.