Spooky stuff: Byron, Donne, Shelley, Goethe and Owen all experienced the phenomenon of doppelgängers. (Link to Lord Byron's story on Futility Closet; see other poets' experiences at the bottom of the linked post.)
This doppelgänger business is apparently not rare, nor is it restricted to poets. I've myself heard a couple of stories from family members. As with the above poets, the sightings were connected with news of death or childbirth. I wonder why?
Actually, it might be fun to run into one's doppelgänger on the street. Though one may have to employ techniques from this classic scene to separate the real one from the spirt. (BTW, that clip is hands down one of the top 5 funniest sequences in cinema history.)