Hipstamatic has become incredibly popular online: while of course you can instantly share the images on facebook, there are also dedicated flickr groups and other online galleries to check out.
Last autumn, New York Times photojournalist Damon Winter decided to deploy the hipstamatic app when shooting in Afghanistan. Using his iphone was not only convenient, quick and light, it meant he could also work without drawing attention to himself. Additionally, he says that the soldiers were so used to taking photographs of each other on their own phones, that he was able to work without them posing for the camera, as would normally be the case.
You can see the gallery of his Afghan photos here.
The New York Times photojournalism blog is itself an outstanding resource.