OK, listen up people! I removed cat urine smell from my wood floors!
Volunteering for our local animal shelter, I was given two male cats to foster. The cats had had a terrible life and were not normal. I had never had an adult in-tact male cat and did not know about urine marking. One or both of these cats peed and urine-marked in that room for weeks. I noticed a smell and kept changing the litter, but the litter box never seemed full. Strange! Big mistake not to get to the bottom of what was going on sooner. Anyway, in the end this room is my daughter's bedroom in our 200 year old house and it had a TERRIBLE cat smell. I was not going to rip up old flooring!!!! I read dozens of on-line sites about this problem. I tried everything, lots of the ideas listed here including vinegar and baking soda as well as "Nature's Miracle" which was recommended by the shelter. Nothing worked. Then I finally figured it out by myself.
As mentioned in other answers, the urine soaks into the floor. I realized that even liberally and repeatedly applied, all of the liquids, potions, etc. I put on the floor evaporated in a short time. I needed something to soak in like the urine.
Here's what I did. I took all of the furniture out of the room and used a blue light and my own nose on every inch of the floor. I found three places that really smelled. I then poured Natures Miracle on an area about twice as large as each smelly spot AND I COVERED THE WET SPOT WITH PLASTIC WRAP. At first, I put more liquid under the plastic wrap every few days. After a few weeks, I re-wet the spots under the plastic wrap less frequently. After about 4 months (maybe 6 months, I can't remember), I took the plastic wrap off the floor, in humid summer weather, and the smell was gone. (It goes without saying that I tested all of the potions on a small spot before putting on the floor.)
There you have it! I hope someone sees this idea and benefits from it. I haven't taken the time to write this up and post it on all the boards I consulted when battling this problem. So, I'm doing it here today.