I never have.
Just got a new roommate who insists it stays down so her normal, adult cats don’t accidentally commit suicide. Google yielded nothing about this danger. Any of you heard of even one cat dying this way?
So they don’t fall in and drown? No.
So they don’t play in it? Yes.
Then there’s my aunt, who had her cats toilet trained. Naturally, she always kept her lids up.
One of these days, I need to toilet train our cats. Tired of changing litter boxes.
We have 2 cats and have never kept the toilet seat down. Occasionally they’ve shown interest in the toilet but have never done anything more than stand on the edge and look in. Considering how far an adult cat can jump I don’t see how a cat could possibly drown in the toilet. Make a mess, sure, but drown? Come on.
Never worried about our cats’ safety. Keeping them from using it as a fountain, sure.
Compare the size of your average cat to the average toilet, especially the water level. Unless you have really deep toilets or really small kittens there’s no way a cat could drown in the bowl, unless it curled up and went to sleep head down. There’s just not enough room in there.
Plus, as every cat owner knows, if kitty hits the water unintentionally it suddenly turns into 50% water-skeeter and 50% Pershing missile, running on the surface of the water for an instant until launching itself skyward, fleeing the room and finding a warm sunny spot to dry out.
I leave the lid up and the seat down, so they have a nice ledge to sit on while they enjoy a refreshing beverage.
And before anyone goes ‘Eeww! That’s gross!’:
1: The bowls are flushed; cats aren’t stupid enough to even taste contaminated water, and
2: These are animals that regularly lick their own (and others) anuses.
We keep the lids down, but it’s because they are curious kittens and I don’t want to have to clean up the mess. It’s bad enough they’ve discovered the toilet paper…
My cat is far too talented to ever fall into such a predicament. But of course she lacks the common courtesy not to drink from the bowl at all…
If we put the lid down, how could our cat get a drink? I guess it would help eliminate the paw prints on the seat.
I know that kittens have fallen into the toilet and drowned - not sure about adult cats. I would think that most would be able to get out. They might get cholera trying to clean themselves, though…
I have a female cat, so I keep the seat down, but the lid open. She really complains if it’s in any other state.
When my cats were kittens I kept the lid down but now that they are older I don’t bother. They don’t really drink from it but one always falls in when he tries to leap from toilet to shelf. He manages to catch himself before more than toes and tail get wet.
If my cat gets cholera from my toilet bowl, I have far more serious things to worry about.
…like the fact that I have cholera.
(The water comes in treated, so my body waste would be the only possible source of the cholera bacterium.)
We leave it open or closed, as the mood strikes. Let Darwin sort it out. 
I keep the seat down because my husband insists on using those blue thingies in the tank and I don’t want the cats drinking that stuff. They were happy to use the toilet as a water bowl in the past and I never worried about any sort of safety issue.
Having had to give a squirmy kitten a sponge-bath at 3 am after she fell in the toilet (I didn’t have a chance to put the lid down), yes, I can say it’s a good idea.
I’ve never had a problem with my cats, but a coworker’s kittens would frequently get up on the rim of her toilet bowl. Her solution was to shape crinkled tinfoil around the outer rim. It wasn’t pretty and had to be removed whenever someone wanted to use the toilet, but it only took two or three (supervised) attempts to jump on the rim before the kittens learned not to do it.
we keep the lid down so that
1.) They don’t drink from it
2.) They can use it as a “stepping stone” to get into the bathroom window.
I leave the lid off the tank, so the cats can drink from that.
When the movers brought our household goods from Hawaii, we locked the cats (including two kittens) in the bathroom so they wouldn’t get out of the house (or under the feet of the movers). All of a sudden I hear outrageous yowls coming out of the bathroom so I go running in. One of the kittens had managed to fall in the toilet and the other had closed the lid on her - and was curled up on the lid with that “ignore the yowls coming from under me - there’s nothing wrong here” expression on her furry little face. I rescued the poor baby and dried her off - and left the lid down after that.
Same thing I post in the “toilet seat up or down?” threads - in a male household, a female househols, a mixed household, a household with cats, or a household without cats, I keep both the toilet seat and lid DOWN. That’s what the lid is for.
We try to keep the lid down mainly because one of our cats likes to sit on the lid whenever anyone is in the bathroom using the sink or shower. (We keep a bowl of water in the bathroom for any cats who happen to wander in there looking for a drink of water.) The other cat likes to try to catch brown “fishies” in there, so we close the lid just to make sure he doesn’t imagine seeing them in there and decide to dive after them.
In all the years I’ve lived with cats, I’ve never known a single cat to jump into an open toilet. I’ve known even fewer that have drowned as a result of doing so.
In fact, the cats I have been familiar with are smart enough to check to see whether or not the lid is down before they jump up there, or they are smart enough to make appropriate adjustments on their way (or, like the current toilet- sitting cat, they are smart enough to jump up to the bathroom counter to observe the current state of the toilet seat before jumping down onto the toilet).