If someone I knew IRL found me on here then I would rather they DIDN'T tell me, as I'd be very embarrassed about it!
I never post anything too personal, so it's not that there's too much info out there, but I would prefer not to know if someone suspected who I was.
I did meet someone IRL who was on here, but I didn't tell her. I didn't know her very well, and she was someone I met at a coffee catch-up after a mum and babies exercise class. We'd met a few times after that class, but then she stopped going. Her baby had quite a distinctive name, and she posted on here about the class she attended (luckily she didn't say she hated the women who went, or anything like that...)
I saw on here that there had been personal things going on in her life, which I assume is why she stopped going to the class. If I knew her better I would probably still not have told her. I think it would be quite creepy, and an invasion of privacy.
It's a bit like if I knocked on a friend's door and saw them naked through the window. I wouldn't tell them, and would pretend not to have seen, to spare any embarrassment. I'd hope they would do the same for me!