I carry my iPhone with me wherever I go, and often, my DSLR and at least two lenses. I often use my phone's camera for taking notes, quick photos to send to Twitter, etc, but I still like having the dials, controls, and depth-of-field provided my actual camera...
My heavy, bulky, likely unnecessary camera.
At least, so says Objective Scenes, a "a group blog dedicated to the art of mobile photography. All pictures are shot and edited exclusively on mobile devices (iPhones, Android, etc)."
The photos aren't always straight uploads from one's phone; the collective often employs, to great effect, the oft overused Instagram and Hipstamatic apps.
Still, they proven that sometimes, perhaps often, the limits of the tools we use often lead to the greatest creativity.