Another health-related website that I frequent has an area within the member profile titled City/State/Country.
Another area of that website has a map and asks you to mark where you are from. Pretty cool to see there are others that may be in faraway lands that you never knew existed, while others may be your next door neighbor.
For those who live close, it is nice to share local info about recommended doctors, and other treatment providers.
Some have even formed local "meet and greet" informal get-togethers with others from the message boards/website.