Regarding optical size of icons... for years I've wished that icons were sized (in the dock, in Finder, etc.) to consistent maximum area on top of maximum height/width, so that applications with square icons wouldn't look bigger than the circular or irregular ones. It would make everyone's dock look so much better.
For example, a 32 x 32 icon has 1,024 pixels. If we declared than any icon can only use 2/3 of the available area, then square icons would be reduced to 26 x 26, circle icons to 29 x 29, and more irregular shapes like a printer or magnifying glass would presumably get the full 32 x 32. It's trivial to sum up and calculate from the amount of transparency, and would leave rows of icons so much more optically balanced.
(More advanced -- to deal with hollows, you can "shrink wrap"/"gift wrap" the icon before calculating area.)
Visual weight is not just about number of non-blank pixels. The author has a few good examples of how strong colours add weight to otherwise identical icons, and so dark icons look better being a bit smaller.
For example, a 32 x 32 icon has 1,024 pixels. If we declared than any icon can only use 2/3 of the available area, then square icons would be reduced to 26 x 26, circle icons to 29 x 29, and more irregular shapes like a printer or magnifying glass would presumably get the full 32 x 32. It's trivial to sum up and calculate from the amount of transparency, and would leave rows of icons so much more optically balanced.
(More advanced -- to deal with hollows, you can "shrink wrap"/"gift wrap" the icon before calculating area.)