Read about a great idea for geo-location app, Echoecho (name so nice, you say it twice?). Unlike Foursquare, where you just broadcast your position (or not really broadcast it, by staying “off the grid”), here you get requests for your position.
You can always say “no”, of course, though I imagine this app is most useful for locating friends while doing, say, a movie or a party. Like calling someone up with “Hey, where are you?” except without the calling and with a neat mini-map, showing actual location.
I think Echoecho should co-operate with Evite and other invitations services — so that participants could be automatically “pinged” in one swoop, and a map with their locations would be a great visual aid to see at which stage your group moviegoing is right now.
p.s. Here’s a link to Echoecho app’s screenshots for Android version, with mini-maps.