Sara asked about spinning standardized yarn for socks. For many years I did serious technical spinning and made oodles of standardized yarn. Alden's class on Spinning to a Standard is essential, and his techniques make replicating a particular yarn or repeating your own, consistent spinning very, very easy.
Stephenie can recite the various margins for error in grist that amount to a significant change in gauge or sett. Coarse singles definitely show the difference far more than froghair! My goal is usually to keep within 5% to either side of the intended grist. It takes a level of concentration and intention to achieve that, but it is definitely possible. Ideally, the fiber itself is unvaried, something like a Janet Heppler fleece (lovely, consistent stuff!), prepared the same throughout. To repeat a particular level of lumens, I spin for the same hours each day, using one bobbin, winding off onto storage bobbins. When the entire batch of singles is complete, I ply, and I try to do it all in one afternoon. If at the end of the process I've got a few skeins that are outlyers, they become cuffs or facings.
I don't expect the various sock yarn manufacturers to standardize their product, but I do find myself pondering making a table of equivalents to ease substitution. I used to have a bright green yarn guide booklet -- has anyone updated it? One of the things I enjoy nowadays is how diverse the selection is at a good LYS, but it really is a bother for socks. My goal is a perfect fit, plus I appreciate the efficiency of being able to pull a pattern card out of my box and grab a yarn that is an appealing color and whip out a pair of socks. I've begun storing sock yarns in bins sorted by grist, and I'm paying much closer attention to ball bands now when I buy yarn.
For Annie, a quick scan of an orange toe (complete with markers in case I have to rip and re-knit after the final fitting). The Patons Kroy orange is coarse compared to the grist of the Fortissima gray, but for a toe it's not much of an issue.