Latch

...so to speak

I read the post of another user on here that I know (of) from another website I go to. This is the first time it's happened to me, and it totally surprised me. I didn't know he went on here, and he doesn't really know me (I lurk quite a bit on the other site too). The two websites are totally unrelated. Anyways, has this happened to other people? I don't mean you refer someone to another board or site and they go there to.. but I mean you go to another board/site and recognise someone else based on their username/comments/whatever.