Am using the APIs from twitter, instagram, foursquare and youtube to get the data. Google maps api to display the map, user locations, directions, etc. and the yahoo placefinder api for geocoding and reverse-geocoding. Everything is done client side with jquery, backbone.js and handlebars.js

EDIT: You don't need an account from none of these services. rround just uses your location and the rest is magic ;)

I forgot to mention that it also uses local storage to show you the people that were rround you on your last visit.