Not our Lotta. See post #30.
Down
Always been that way in our house - Mother’s Rules and no one disobeys Mother.
Also we’d a cat who would drink the water, and I didn’t want her to drown or anything.
And also, lived near a block of flats where a woman claimed she found a rat climbing out of her toilet.
Lid down. Because I saw that same TV show about dirty stuff spraying out of the toilet when you flush, and I have a cat. I don’t think she would jump into the toilet, and she has never demonstrated any interest in it, but I don’t want to take the chance.
I also like to put my foot on the lid when I’m putting lotion on, which would be kind of hard and disgusting if the lid was up.
I’m a guy; putting the seat and the lid down was the agreement my wife and I came to regarding toilets. To use my brother-in-law’s argument; you you’re done using a jar of peanut butter or jelly, you’d close the lid wouldn’t you? 
My preference is for lid down for many reasons: not impressed by seeing the interior of toilets, makes it useful as a seat, fear of pets falling in, fear of other stuff falling in, etc.
My spouse (male) seems to prefer leaving it up. Given that he occasionally has OMIGOD URGENT!URGENT!URGENT! episodes this is partly for ease of access Also, I think he just doesn’t think to put it down.
We’ve agreed to stop arguing over the matter. Leave it as you want, and reconfigure as needed when you return.
I keep the lid up. The seat is always down unless I’m cleaning the toilet, as there are no males in this apartment.
I keep it up. I’m sure I’m not fooling anyone by keeping the lid down because “it looks better”. Oh ya, they know what’s going on in there. There also seems to be an inordinate amount of men who are married to women that have lost the use of their limbs, my condolences.
Just because I prefer the look with the lid down doesn’t mean I’m trying to “fool” anyone. It’s just a preference. I’m not pretending there’s some great advantage or objective beauty in that configuration.
I know what people do with/in/on toilets, too - that doesn’t mean my preference to NOT see them actually doing it indicates any type of “fooling”, either. It’s a totally natural process that generally leaves one feeling better afterwards than before, I’m all for it. I’d just rather not see it.
I put it down to make sure the dog doesn’t drink out of it. Also as in the escaping inanimate objects thread, it keeps them out of the bowl.
This, but I’d like to add if it was down when I got there.
Also, I’m female.
Male, down. At my place, I’m just not interested in providing an extra water dish / bathtub for the cats. I do it everywhere else just out of habit now.
Lid down!
My husband always seems to leave it up, but thankfully he remembers to put the seat down, so that’s something.
Had to laugh at Corkboard’s sonic toothbrush comment–those loose-fitting toothbrush head covers always pop off and always seem to head right for the toilet…uck.
And since I keep my makeup on a shelf above the toilet, if the lid is up, I can plan on some pencil, container, brush or something plopping into it. Sigh.
At home, always down. My wife appreciates my doing so.
In a public restroom, always up. If every guy left the seat up in public restrooms once he was done, we’d never have to clean piss off the seat before sitting on it.