The breeder I'm getting my new kitten from starts toilet training, using the Litter Kwitter system when they are quite young. Though they always have the option of using the regular litterbox as well.
I won't be continuing his training as I believe it's natural for them to dig and cover their waste. I think I've also read it can cause arthritus as it's an unatural squating postition, but I may be wrong about that.
If you search the forum there are other threads about people who've toilet trained their cats.
I have 2 that want to use the toilet, but can't quite figure out how. There has been urine on the floor around the bottom of the touilet several times, so I think someone is trying. I would love to have one of those training things, but I have not been able to find one at out local pet stores. I know I could order one from somewhere, but I would like to be able to actually look at it before I buy it.
My bf tried to toilet train my two kittes at the age of 5 months and it didn't work so well. I think if he had bought the Litter Kwitter, it probably would have been successful but he bought the Citikitty which is a piece of cheapy plastic and got my two kittens more scared than anything. The CitiKitty doesn't fit well nor support well once placed on the toilet seat. The cheap thin plastic makes sounds that they didn't like. After a series of accident on their blankets and bathroom floor, we gave up. I was never for the toilet training to begin with.
Our 6 year old Jonesie is toilet trained and I am currently in the process of toilet training our two new Devon Rex additions to the family. It's messy for a while, but once they get the hang of it, it is surely worth the effort!!!
There is a yahoo group that has lots of information on the subject: