Now that I met Peter Rukavina, I am involved in the Plazes development effort.
This blog post explains what Plazes is. Peter does it, too, at his Rukapedia.
In the bar at the right-hand side of this page is a little location notifier, which says something about where I’m at. That Plazes data. It’s free!
Like hacking? There is an API, and a friendly community of developers out there at codeplaze.com.