Since I got the iPhone 4S I've been doing most of my personal shooting with it. I'm really impressed with the quality and enjoy the limits of the square format that Instagram sets. Shooting like this also frees me of having to sit down to process photos, which usually takes a long time because I obsess over them until I'm satisfied. In a moment of clarity, I summed up my feelings about shooting with Instagram in a message to @photojack: For me, it helps let go of the idea of "perfect," allowing me to enjoy the results of the moment and move on.
I sometimes feel guilty about shooting with a "phone," but what matters to me is that I always have it with me and I'm getting good results with files that I can print at a decent size. I've started making prints for Art-A-Whirl and am also using some iPhone photos for a project I'm working on. More on that in another post.