Here's the weirdest thing of that nature that has happened to me:
I was walking around on campus at UK one afternoon, when I hear a stern voice behind me call out: "Cadet Osborne, why are you out of uniform?" This really gets my confused attention because I'm not a Cadet, but my last name is Osborne.
I turn around and there is a somewhat upset ROTC instructor standing there, he looks stern at me for a moment, looks closer, then his eyes widen and he apologizes and says I looked just like one of his cadets.
Now, the weird thing was, I was in the ROTC for a while, about two years before this, and apparently now there was someone on campus who was a near doppleganger, with the same last name, and was an ROTC cadet (while I was a former cadet).
To a lesser extent, I once have a friend come up to me and ask if I know anything about a certain odd font he found online, an alien script from an old Star Trek episode. I said I knew a little about it, and I asked why. Apparently some screen captures and research I did based on that script to figure it out (about five years prior) that I e-mailed to somebody I was talking about it on rec.arts.startrek.tech was turned into a font of that script. He gave me full and prominent credit on his web page, but it was just kinda creepy to see that an email exchange from years ago had turned into a web page crediting me, and a friend finding it independently and pointing it out to me.