3. What type of kitty litter are you using? It's the same thing as the doona. If your cat doesn't like the feel of that particular type of kitty litter then he is less likely to use it all the time. Sometimes it's trial and error and you have to go through a few different types to find the litter that your cat prefers.
Aussiegirl has reminded me... when we first got the boys, I was using crystals - which they hated. Considering they kept going on the doona / clothes / pillows etc, I opted for the recycled paper kitty litter... anything that had a similiar feel on their paws. Since we changed to the paper, we've had less accidents...