I've had 2 littermaids in the past 4+ years. I have 3 cats that use it regularly (including the one who is living 60ft up a tree currently). I destroyed the first one when it was about 2yrs old by accidentally getting the motor wet.
The littermaid directions say NOT to use litter that has crystals in it, so I use a clumping litter with no crystals. I have found the best (and I've tried most of them) is Scoop Away for multiple cat households.
I have never seen it try to come on when there is a cat in the box, so I'm assumming that the sensor was doing it's job.
With 3 cats, I generally change the receptacle 2-3 times a week.
The biggest factor is keeping the litter level to the right level, if it gets too low the scooper can't clean correctly.
I only have to take it apart and scrub it every other month. Other than that, I just clean the exposed areas with spray cleaner and a paper towel once or twice a week.
Hope this helps,