Over the years, I have gathered much useful information from the nutters and other strangers who just up and start talking to me. I used to think it was because I was a cute young blonde, but the rate of stranger-attraction increased steadily as I grew older. Now that I'm 57 years old, I can find myself in conversation anywhere, with just about anyone.

VT is right; it has a lot to do with eye contact -- if you look at people as if they are already friends, in a few minutes they will be nattering away if they have half a chance. It happens most consistently on public transit, but also in line anywhere, especially the checkout in the supermarket.