I think the "location" implicit social graph is just one of many. It might be the easiest to grok, but it doesn't strike me as the most useful.<p>I like Fred's example of people with similar music taste on last.fm. I like the idea of being connected with people who will attend the same event as me, or an event I wish I was at, or whose netflix ratings correlate highly with mine.<p>I would imagine that eventually, the <i>explicit</i> side of things will more be addressing the privacy issue you mention. But really, I want my graphs to be generated for me with the least work possible.<p>Instead of a social dating site, what about an implicit social graph approach: show me people in this coffee shop who are open to being approached for a brief chat. Show me people in this city who are willing to grab a beer with a stranger in town for the night who have similar interests.<p>Lots and lots of interesting stuff will become possible as we start to master all the information and implicit connections available out there even today.