We have several very mature post oaks. Most of the falling leaves have something pink and fuzzy attached. The pink things are solid (dense), and when broken open are white inside. I saw the image of oak galls in the Library, but those are small and smooth. The stuff on our trees is bigger than a pencil eraser, compact, furry, and a washed-out pink color. It seems almost every leaf has some. What's going on here? I'm not sure yet whether our cedar elms, pecan, or hackberrys have the same pink nodes on them.

I'd guess that it is still a gall. There are many many types (sizes and shapes) of galls; that is a reaction to an insect bite or sting on the plant leaf, that it forms this type of growth around it. Have you had these before? Often times they are more prevalent some years than others.