All I know is that cats walk on their toes. When you declaw, its removing their toes and causing their whole body's alignment to become out of whack.

As for scratching, I provide several scratching posts. They have taken to scratching the couch, but I've never corrected them because I HATE that couch... perhaps we'll get a new one faster They don't scratch anything else in the house. I have some nice pieces of furniture in the same room as the couch and they've never once laid a claw to any of them.

I keep their nails trimmed, and its not a major thing to do so. I've found some catnip before a trim does wonders for their agreeable-ness during the trim

Please collect the data people will post. Read the information and make the best decision for you and your cats - not your furniture. I've seen people who have done it because they wanted to preserve their possessions, but spent more afterwards for follow up vet visits, behaviorists, medicines, etc. than they would have for a new set of furniture.