I have owned the Littermaid for now about 2 years and really appreciate how well it works.  I often forget that I need to empty it out and the little liner is usually packed full.  I have found that the plastic liners are a bit fragile, so I took some 2 inch packing tape and wrapped it around the fringe of a new plastic liner.  Since then it fits better and doesnt warp or crack when replacing.  I also can give it a little spray of cooking oil so I can wash it out and reuse it during the next empty.  Using this technique I have only used about 4 liners in 2 years.  I have had pretty good success with the Arm and Hammer brand of clumping litter, and DO NOT buy the little "balls" of the new litter, plays havoc on the machine and they end up clogging and popping around all the time increasing the noise and Im sure the wear on the machine.  This is definately a ONE CAT machine, my cat is so facinated with the device she's in and out about 2 times an hour, so with more cats I can see how the machine would drive me insane.  I think I am used to the noise, though I stash the device in the laundry room so its not too bad.