I took this photo up in Banff Canada of this lake that looks like a fox with my iPhone, Nokia N82 and Nikon D80. Here are all three for comparison:
The iPhone is really great for taking photos at the spur of the moment. The colors are vibrant, and when viewed ON the iPhone they look great. After posting them to flickr, you can see that some detail is lost. In this example in the mountains.
The N82 is a 5 megapixel camera, and also has a nice Xenon flash which makes it great for taking photos inside where it/s dark. It finds focus pretty quickly. The image has greater detail than the iPhone, but in this image the colors might be a little washed out.
Note: The N82 found focus faster than my N95, but that could be because I haven't upgraded my firmware on the N95...
The D80 has fine detail in the image with great color. It also allows for a wider angle, bringing in more of the foreground and side, for the best composed shot.
Benefits of the iPhone / N82 over the D80, is that you are connected via the cell network or WiFi and can email and/or send you photos over the internet to friends or photo sharing sites like flickr.