I have been following with great interest the differences between the Nikon D800 and 800e and every few days more information and or examples come out. There are some things that can be said about any comparison of photographic equipment:
1) it's never as easy as you think
2) there are many factors which will result in a less than helpful comparision - ie. apples and oranges.
Imaging Resource just posted the 800e studio image - so a chance to compare cameras with identical images, same lens, steady lighting, tripod etc. The 800e did not show a huge advantage. Other 'identical' comparisons had shown a bigger difference. It's essential to consider whether the image is a jpeg straight from the camera or a jpeg that came from the raw file. We also need to consider the lens used. In the case of the Imaging resource comparison, it's the 24-70 mm. Nikon lens - good for a zoom but definitely not up to a good prime lens, even the relatively inexpensive nikon 1.4 G, and certainly not the chart leading Nikon 85 1.4 G.
Today, digilloyd (for a fee) has tested sharpening to see what level of sharpening could possibly result in an 800 image looking just like an 800e image.
at GetDPI.com the Nikon forum has a lively discussion going on whether with extra sharpening the 800 images will look (and especially print) just like the 800E images.
For what it's worth, here's my observations after looking at and printing images:
You can only see the difference between the 800 and 800E if you start with a really good lens, optimal aperture and perfect technique - once you have to sharpen the 800E image significantly, it's hard to differentiate from an even more sharpened 800 image.
In prints 20X30 from a top lens I can see a difference between the 800 and 800E - but I doubt that the public could. At prints 49 inches wide (200% or 150 dpi) I think anyone could see the difference, but it's not huge even then - just less sharpening artifact.
Bottom line - you have to look for the diff. in the E, but with good glass and big prints, it is there.
To generalize to other comparisons:
minor change in the position of the sun (especially if it is glancing the subject) can affect apparent resolution and microcontrast and negate any camera differences. Less than stellar lenses won't show subtle differences in pixel count or presence/absence of an AA filter. Where the image is focusesd can make a giant difference - even minor variations can negate an otherwise useful comparison. Curvature of field can really screw up assessments. A number of lenses, many fast lenses and some others (like the 14-24 nikon) have sig. focus shift as you stop down. If focus was obtained wide open, even by live view magnified there can be errors creeping in. As for auto focus - well there are complaints all over the net about difficulties focusing with the latest cameras. Those who shoot for pictures seem happy, those who shoot for tests not - which should tell us something. Again, focus curvature may have a lot to do with the apparent errors seen with lat. focus spots.