Instagram App
Anticipated social app that let you share emotions through photos. Instagram gathered 100,000 users in their first week and that's I think is because
1) most iPhone users already have several photos that can be shared online
2) Photos are universal
3) well integrated with social media such as twitter, facebook and foursquare
4) UI is beautiful. Useful effects are built into their iPhone app. Photos look great
The issue now is how they can retain user attention. So far they have no game elements such as foursquare's batch. I'm looking forward to see what is going to happen to them
I think so.