Of course if someone really didn't want to share a toilet seat with their cat they could spend some big bucks (not sure how much they cost) on a Sani-seat!

http://www.cleanseats.com/

It's got a sensor to put a fresh new cover on the toilet seat when you swipe your hand by it. I used one at my urologist's office yesterday. And it seemed to have a little timer built in where it wouldn't just rush through the seat covers. I wonder if a cat would be interested in standing on the plasticy feel of that seat cover..