Here are a few ideas, some repeats from above:

1. Trim your cats' claws. I use these scissors from Pet Edge:
http://www.petedge.com/product/Maste...sors/44495.uts

Just make it a Saturday (or some other set time) chore.

2. I'm not sure about carpet. But for furniture this is what I do:

a. have plenty of scratching posts around the place. Now and then, rub some catnip on to remind the cats those are THEIR places.
b. same time you rub the catnip, mix a spray bottle with equal amounts of white vinegar and water. Spray the furniture edges, or where they try to sharpen. The mix is dilute enough that we humans don't smell the vinegar, but the cats do.
c. buy some double sided sticky tape at a craft store, and put that on the furniture edges. Cats don't like having their claws stick and slow in the sharpening process, so they don't go back there.

Hope this helps!