Whrrl for

From Pelago, Inc.:

Whrrl lets your friends light up your map based on the places they go in the real world. You can zero in on what they are up to right now, plus their past visits and ratings highlight cool places for you to go. Share your current location and find your friends using the iPhone's built-in location device. Remember places you want to go and display them on the map at any time. Filter lists of places with only a few touches. The more friends you add and the more places you rate, the better the recommendations and the whole Whrrl experience. Whrrl also makes it easy to invite friends right from your iPhone address book or via e-mail address.