This story isn't as extensive as the others, and it has taken a while to pull it together, in part because I have a poor memory and I had been conflating two different people (when they were the same person, it was a better story; unfortunately, I can't let a good story stand in the way of the facts...). Now I have it sorted out, however, and I'll tell the part that involves Jon Riecke.
You can look him up on the web; he's been at Aleri in NYC for nine years, and the previous nine years he was at Bell Labs. Before that, he spent a year as a postdoc at UPenn, after getting his Ph.D. from MIT in 1991. He's basically my age, although in "advising genealogy" terms he's my uncle: his advisor at MIT was Albert Meyer, who was also my advisor (John Mitchell)'s advisor.
Since this occurs in the world of computer science, I should invoke the whole graph-theoretical "six degrees of separation" business; however, since our end of CS isn't very big, I won't detail all of the connections between Jon and me, in terms of chains of co-authors, joint attendance at conferences, etc. There's a fairly tight network there, but that's not surprising.
I got to talking to Jon at a conference, because of these mutual connections, and was interested to find out that I had essentially taken his place at UPenn -- I had been a postdoc there the year after he was there, occupying the same office (and probably the same desk). We started exploring our backgrounds, and he was interested to hear that I had attended Northwestern as an undergrad. He said that he had a good friend who had gone there, whom he met while camping at the Philmont Scout Ranch in New Mexico. I had also been a Boy Scout, though I had never made it to Philmont, but I asked what his friend's name was. It turned out to be Steve (I'll omit his last name, because it doesn't really matter for the story), a guy that I knew from the Film Board. My wife was there, and she pointed out that Steve had for a time been dating a good friend of hers!
So, those are my small world stories. There are others: encounters with people who played my old position in various handbell choirs, intricate webs of connections among people in small towns, etc., but none of them are as extensive or startling as these. In fact, that's one of the things I like about living in a small town now, that you can keep bumping into the same people in lots of different ways. Now we'll see if putting these up on the web (admittedly with no promotion whatsoever) might lend some of that small town feel to the Internet -- who knows, maybe someone will stumble across this and say, "hey, I know you from ..."