David Pogue ran a test:
On the show, we did a test. We blew up a photograph to 16 x 24 inches at a professional photo lab. One print had 13-megapixel resolution; one had 8; the third had 5. Same exact photo, down-rezzed twice, all three printed at the same poster size. I wanted to hang them all on a wall in Times Square and challenge passersby to see if they could tell the difference.
Even the technician at the photo lab told me that I was crazy, that there’d be a huge difference between 5 megapixels and 13.
Bottom line, no one could tell the difference: “I’m telling you, there was NO DIFFERENCE.”