Interesting to see Nokia still developing their Friend View application in the light of the elephant in the room, Google Latitude (though as even that can't seem to get traction, what hope has Friend View got? - discuss). The latest build of Friend View has background notification features, in that you can leave it lurking away in the background and it will ping you when a friend gets within a customisable distance from your current location. See this Beta Labs Friend View post for the full explanation and some handy shortcuts.