I was at Web 2.0 Summit last week in SF, and was wandering around downtown trying to meet my friends for dinner. I had my Blackberry with Google maps on it so I could see where the restaurant was, but what I really wanted was to see where I was, and where they were in relation to each other. And I wanted to be able to use my phone as a compass, being able to align it to the streets so that I knew which direction to walk.
Then, on the way home, I ran into a friend purely by coincidence at the airport. We got to catch up and have a great spur-of-the-moment visit.
In both cases, I would have loved to have been able to see that I had friends nearby and to see where they were. I would pay for that service.
There is a new Silicon Valley startup called Loopt which is doing exactly this (minus the compass). It will be interesting to see how long this technology takes to hit the larger market.
(Thanks to my friend Joseph for the heads up on this one.)