It is unfortunate that I can speak on this topic. If you have (or had) a cat that sprayed in your house, I have a solution - literally!!!
I scoured the internet for lots of ways to get the smell of cat spray out of furniture and kept finding so many people saying "You'll never get it out!" or "The only way to get rid of it is to buy xxxx solution" Which costs like 20 bucks and it's only sold online and comes from New Zealand (or some crazy stuff like that.) I did find a couple of people that gave up a home remedy that worked for them. There were a couple variations of the same thing and I was willing to try all of them, if necessary.
The first and only one I tried was a solution of about 60% hydrogen peroxide (you can buy a huge bottle of it for only $.88 or so at Wal-Mart) and 40% water. I put mine in a spritzer bottle and sprayed it on the couch. I didn't just lightly mist it, either. I sprayed the crap out of it!! I think the pad underneath the cushion cover was probably sopping wet. I wanted to make sure I got it all!!! I waited a couple of hours for it to dry, smelled it and sure enough, the smell was gone.
Just because one time of spraying worked for me, doesn't mean it will work for you. Who knows, it might not even work - I guess it depends on the strength and age of the cat spray. I say if you tried it once and it didn't work, try it again. If you notice it is lessening the scent, keep going!!
I know that just because the smell (to me and other humans) is gone doesn't mean the scent is gone to the cats but hey, as long as it doesn't smell like cat spray on my couch, I am certainly OK with that.
For more fantastic tips, head on over to Rocks in my Dryer!