I use my iPhone 4 with the Instagram app. Sometimes I also use an app called Color Effects. The quality of the photos from the iPhone 4 camera is superb. Instagram filters are great at correcting lighting or providing filters that I would ordinarily have to spend money to add to a camera.
Plus, my iPhone is always with me so I end up taking more pictures (many of which have made it into my Hubs).
I wrote a hub on using your iPhone (or Android phone) camera to take good food photography, if you want to read more about Instagram and color effects, too.