I've had an OkCupid profile about 10 years, and have answered over 1200 questions in their database.
When I travel, I sometimes reset my location in OkC to be the city I'm in. It makes for an interesting view into the place that I'm at.
When I'm in Seattle, there are surprisingly large number of people who match me at 95% or above. When I am traveling, there are relatively few people who match that closely. Often, there are none. Even in very densely populated areas with an order of magnitude more people to match against.
I find that very interesting.
Did I end up living in Seattle because it's friendly to "people like me"? Or is it the other way around, and being around Seattle has made me more like the people here I match so closely with?
And then there are even more interesting questions one could ask and answer with the OkC database. Does this kind of "lots of close matches" effect happen in every city? How much dispersion is there in a given city? After all, even if there are many people I match closely with, there are a LOT more in Seattle that I don't match at all. How do other cities compare that way?
Hopefully the data geeks inside OkC will someday answer these questions.