Mitigating Contrast Loss From Diffraction aka How to Make f/16 Look Crisp
This is an important read for anyone looking for both depth of field and crisp per pixel sharpness.
While diffraction remains a challenge for high-res DSLRs and the peak aperture for a top-notch lens remains f/5.6 (on the full-frame Nikon D800E), it is possible with appropriate sharpening to greatly mitigate the micro contrast losses. Though there are limits: a low-noise well exposed image can accept more aggressive sharpening without developing uglies far better than a noisy underexposed image.
In Making Sharp Images, as a followup to Diffraction Limits for High Resolution DSLR, I show-and-tell what sharpening can do to mitigate the contrast losses from diffraction.