Interesting points about the toilet training... but I don't agree 100%
I've toilet trained all four of my kitties, including the one that is now 16 yrs old (she was 8 when I trained her).
I do understand his points about scenting, which is why I actually don't scrub the bowls as often as most folks. I also tend to leave one toilet as the exclusive kitty potty. It is true that for a few days after cleaning the bowls, I will get a few prezzies on the floor... but it doesn't last long, and I don't punish them for it. As for scratching, they just paw at the seat and lid, and I don't discourage them from it.
As for keeping track of healthy pees and poos, I actually find it easier with the toilet. I would have never caught Pippin's liver problem if I hadn't noticed that the color of his pee had changed. Also, I can hear how strong a stream is with the toilet, but would never notice a weak stream with a box... there would just be the clump of litter, and I wouldn't necessarily know whose it was. There is no doubt when the organ meat may have been a bit rich, or the bone content a little high; the poop always tells and the toilet doesn't hinder that at all (but it definitely keeps the smell in check).
Personally, I think toilet training is all about how much patience the owner has. It is not for the impatient person. Kittens learn quickly, older kitties take more time. It also takes an understanding, as Jason mentioned, of what the cat's natural proclivities are. They do prefer to be able to smell the toilet. Being tolerant of a slightly messy toilet is my way of "meeting them half way".
Oh yeah... we also have a "people only" toilet.. so keeps the competition down.