I have always loved Lily Tomlin's Ernestine character (possibly because my summer job the year I turned 18 was long-distance operator for the phone company–there was only one then). She did an album called This Is a Recording, and lately I've been remembering one of its tracks: "The Marriage Counselor." Ernestine listens in on a call a man is making to Korea, where he was stationed during the war, and tells his wife that he has a son there. "…Mrs. Norman, I am so sorry that you had to learn it this way, but we at the phone company do like to keep families in touch."
I don't know to what extent the various phone companies still perform this function, but Ancestry.com has been doing quite a good job. I've discovered cousins in England and Sweden–and then there are the odd discoveries that nobody alive would talk about. And speaking of where Dad was stationed during the war, I discovered that one of my friends was not, as previously believed, the oldest child in the family.
I've just come back from Salt Lake City; I was there for CONduit, but the con hotel is two blocks from the Family History Library, so I got in a bit of research after the con. One of the things I did manage to find was immigration dates for two of my great-grandmothers. The method of calculation starts with "she got married on this date, so she arrived in New York before this." Then I take the date of birth of the first child (five months after one wedding and six months after the other), count back nine months, and then add a couple of months for the couple to meet and start their family. From that point I started going backwards through passenger lists, and found both of them within three years. Unfortunately I wasn't in Salt Lake City long enough to follow them back to France and Germany, but there's always next year.
I also found marriage dates for both of my brother-in-law's grandparents, entered them into the family tree, and promptly discovered that one couple married in December of the year that their first child was born in July.
I suspect, however, that it will be a long time before I find a story to top the one I got from my Swedish cousins about my 3rd-great-grandmother Sofia (1824-1866). Although she never married, over a 19-year period she bore six children to three different fathers. (My 3rd-great-grandfather died in jail after the third one was born.) While illegitimate children were fairly common in rural Sweden–if you're going to live on a farm, you'll need children to help with the work, so you want to be sure you can have them before you marry–Sofia is a rather extreme case. Certainly my grandmother never mentioned her to me, and I strongly suspect that Sofia's son never told his children about his mother. He may not even have told his wife–Sofia died four years before he married. I'm certain he never imagined that centuries of Swedish parish records would be digitized and put online so his descendants could find out the secrets he took to his grave.