I think I understood the source of popularity of the service Instagr.am. I was seeking for this knowledge several months. And now, I am close to understanding as never before.
The receipt of its success is following:
1. get the key point of modern youth movement Hipsterism – Ironic Nostalgia.
2. mix with modern social networking habits
3. add support for smartphones
4. flavour with filters, which might make things look older.
and you get the service, which reflects modern subculture and brings some money for creators.