That Ashley/Cicala/Zenfolio article is excellent. Roger's summation at the end is probably the most valuable:
"1. Anecdotal reports suggest that wide-angle rangefinder lenses exhibit more noticeable field curvature than SLR lenses. This may be because of differences in rangefinder focusing or because few rangefinder lenses are reverse telephoto design. (Reverse telephoto designs have more lens elements, giving the designer more opportunity to correct field curvature.)
2. The actual curvature is improved to some degree, and often changed in shape, by stopping down. Of course, increased depth of field helps mask field curvature.
3. Field curvature increases as the square (3rd order curvature) or 4th power (5th order curvature) of the distance from the center of the lens, so it naturally is more severe toward the edges of a full-frame image. Lens designers know this better than us, though, and use their tricks to minimize this – which results in more complex curvatures affecting the mid range, etc.
4. A given lens may exhibit different curvature at different focusing distances.
5. Taking a few controlled photographs and evaluating them with a bit of pixel-peeping will give you a good idea of the field curvature in your lens.
6. The lens’ MTF chart, particularly if it shows a ‘dip’ in the mid range or widely separated sagittal and tangential MTF, may hint that a lens has field curvature.
Now the truth is that the majority of lenses these days exhibit very mild field curvature, if any. But there are certainly a few that do and those few tend to be superb wide-aperture prime lenses. If you have one or two of those, taking a few minutes to evaluate the pattern of its field curvature (and I still prefer the term ‘area of best focus’) can improve your photography."