There were two moments when this serendipity has been most obvious in my own research:
When my cousin visited the Brooklyn Historical Society and discovered that the person who had signed the sign-in sheet earlier that evening had given her home address as exactly the house we were researching. This netted us a fantastic trip to and tour of the old family homestead.
When I learned my great-grandmother's full given name and discovered that my dad had managed to name a daughter after his grandmother, like he wanted to, without realizing it until she was 21 years old.
I know I'm not alone in having these magical, sometimes chilling experiences. And so I'd like to invite you, my readers, to submit your favorite stories of genealogical serendipity, to be shared (with permission and attribution) in the series I plan to run this Spring. You can submit stories in the comments or via e-mail (kathleen.scarlett.ohara AT gmail.com). Please include a link to your blog, if you have one. (If you're interested in writing a full-fledged guest post about your serendipitous experience, let me know and we can talk about it.)