Ask HN: How useful are these "ambient apps"?

That's all I hear these days. Many teams are out there to "re-define social networking" by incorporating geolocation, mutual friends, common interests based on the FB social graph using push notifications to connect you with relevant contacts. Apparently many people in the valley hail this as the "next big thing in social networking". Highlight was hyped to the hilt only to get mediocre responses.

I'm based on the EC so there're not many early adopters here, so I would love to hear your thoughts. My question is, have any of you actually used these apps, cared to met someone at a nearby location and felt connected with this person to be your new friend? I just don't see how these apps can provide enough relevance for me to go out of my way and meet up with a stranger, who in the worst case scenario may or may not be a serial killer.