i have the littermaid and i LOVE it. three cats and one box, and it was always clean. with three cats i had to empty it once a day, but i recently modified the box by putting it up on a table and cutting a hole in the bottom of the poop recepticle. i put a tall garbage can underneath and now i just have to change the bag in the garbage can once a week or so.... luxury! i found that World's Best, or the litter that is made by littermaid works the best... other clumping litters seem to gum up the works too much.
but about the kittens... i have a young kitten (the fourth cat) who is still not able to use the automatic box, i had to buy one of the regular boxes and put it on the floor for him. i think it was because the automatic box is too clean. you know how they tell you to leave a poop in the box so kitty will remember where to go... well, there is no leaving anything in an automatic box.