This app uses a more easy way of finding others location,not like foursquare, PickMeUp is more pricise on giving out location info and direction to the exact location. Eventhough its mainly about sharing location to people,foursquare has its own UI which is interesting and you can earn points,badges and get to know places nearby with lots of discount.
There are still some bugs that are not fixed in both of the app but foursquare is much better in UI then PickMeUp and foursquare has a better 'social-like' UI. But eventually,both apps are quite usefull for our mobile phones. There wont be any regrets having these kind of apps. Also,have a look here on reviews about both apps