Here it is the 50D, what's next?

[Jon Ruyle]

Funny how small pixels get such a bad rap. No one ever says "the optical perfection of such and such lens is actually a disadvantage, because you need higher shutter speed/smaller pixels/larger aperture/better focus/etc to to take advantage of it." But people make the exact same argument about small pixels all the time.

For example, anyone shooting 5 micron pixels at f/32 because they really need DOF (e.g. macro) is not going to get any benefit from smaller pixels: the returns will be close to 0%.

In theory, one could use high pixel density to do better post-processing. For example, if one is willing to deconvolve diffraction, I believe more resolution is always better.

[Daniel Browning]

In theory, one could use high pixel density to do better post-processing. For example, if one is willing to deconvolve diffraction, I believe more resolution is always better.
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Agreed. If sensors were advanced enough to record the actual phase of the light, then diffraction could be deconvolved perfectly (in theory). But as you point out, even without phase it's possible to get really nice results. High noise power at Nyquist can reduce the effectiveness, so it's more beneficial for low ISO shots.