I think the oddest coincidence in my tree (and there are a few) is this.
When I was a child we lived in a beautiful old farmhouse in the country. Because I was obsessed with history I wanted to find out more about the house. I got to know the details of the family that lived there and when I was old enough went off and found stuff out about them. I knew their names, where they were buried - everything.
I've been doing my family tree for a number of years and started a line a few years ago which was my father's mother's ancestors. We knew they came from North Lincolnshire but nothing else. I was really surprised when I found out that in the 1860s, three of the sons (including my gg grandfather) moved to the village in South Lincs where my father had farmed for 40 years and indeed were farming the same land. This farm had been bought in 1969 rather than inherited and Dad was really shocked to know that his own ancestor had farmed the land 100 years before.
Even more of a surprise was my gg grandfather's third marriage. He married a daughter from the house that I grew up in!!!