Three that I can think of. Feels like I'm forgetting one other one...
First was a long-time poster [outnfree] mentioned my family's name in a congregation thread. My parents had studied with her sister. She studied with another woman in our cong.
Second was I stupidly mentioned someone's real name in a non-private bethelite thread. That person has a unique name and professional customers that googled his name saw my thread and asked him about it. He decided to check out this site, found me and I apologized profusely and had the offending post removed. (I think this actually worked out well, in the end. But I was sure embarrassed to have outed him in the first place.)
Third was someone who's house I was assigned to for bookstudy. We both posted in the same thread something unique about one of our elder's famous children. From our posts, it was clear that we were in the same hall at the same time.
Another few people knew people from my old halls but did not know me (and I did not know them).
I keep looking for more people that I might know; still hoping to find more old friends.
-Aude.