Changing the User Setting "Default Distance Units" doesn't only change the distance units for the Spatial tool. Bizarrely, it also changes page margin specs in the Render tool, and Height and Width specs in tools like Layout.
Separating "Distance" units from "Layout" units would be useful. I may want a map showing kilometers, but when I'm laying it out on an 8.5 x 11 page, I want a half inch margin...