I’ve long stopped using the highest settings on my cameras because there’s really no quality difference that I can tell other than when I want to zoom in and crop a piece.
On cameras, we need a new spec to help us know what quality image we can expect.
In the meantime, check out this Ars article on the topic:
http://arstechnica.com/gadgets/news/2009/03/why-weve-reached-the-end-of-the-camera-megapixel-race.ars