Here's a nice analysis of what makes today's Internet services tick:
Dopplr can show me when a distant friend will be near and vice versa. Twitter can show me what my friends are doing right now. Wesabe can show me what others have learned about saving money at the places where I spend my money. Among many other things Flickr can show me how to look differently at the things I see when I take photos. And del.icio.us can show me things that my friends are reading every day.
It's all about making connections, creating a community and finding a commonality. The post calls this "surfacing coincidences" but I think that "coincidence" is the wrong word, since it suggests something random and casual; what we're talking about is an action that is much more directed: people looking for like-minded, like-thinking, like-doing people. (Via John Battelle.)