So here's how my life works sometimes.
The girl I've been seeing, I met more or less randomly off a dating site right before I unsubscribed. Second date or so, she mentions a friend with an unusual name that I recognize, and it turns out she's an old college friend of his from way back.
She comes with me to Kelly's housewarming party. She gets to talking with the grad-student doing an internship at my company, since they seem familiar to each other; it turns out they were both in the same hut in some town in Laos seven months ago, talking to a guide about backpacking trips, she with her friend, and he with his family.
I gave my Flickr URL to a cow-orker I'm friends with, who added me as a contact; when I looked at her contact, I saw a nickname I thought I recognized, and a little research confirmed that it was, in fact, a girl who answered my craigslist ad back in 2004, and we went out a few times. Turns out she's good friends both with that cow-orker and one of the women in QA.
I spent last week at an aikido seminar in Glenwood Springs, Colorado. Sitting around outside drinking coffee with a guy, it turns out he went to college with my older brother.
Really. I'm not making this up.