This is called a Vein Pocket Gall.
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These are caused by the larval (maggot) stages of very small flies called midges the results of this insect can be seen by the twisting and curling of oak leaves, often resulting in a hard ridge running down the veins of the leaf, hence the name vein pocket gall.
There are numerous types of gall-forming insects that attack oak trees. They all result in some form of bump, nodule or growth developing on the leaf. Inside this growth is the offspring for the next generation of galls to infect the trees next season.
Although galls look bad they rarely cause health problems to the tree although they can decrease photosynthesis in the tree. The formed galls result in the misshapen leaves. The adult stages of galls are small gnat-like insects called psyllids. Psyllids sting the leaves in the spring as they are unfolding. This sting results in the gall formulation in which the egg is laid. The tiny maggots move to the veins and begin to feed. Later in the summer this egg hatches and the small mature larvae fall to the ground to pupate. Normally this stage is never noticed. Then after they drop to the ground they remain there over the winter and the cycle begins the next year. Several small larvae may be found inside the swollen folds of the leaf. There is really no way to prevent this insect from damaging the tree leaves. Things can come in cycles so it may or may not be as bad next year, you will just have to see.

Thanks so much. Now it all makes sense. So, is this something I should try to treat? When I ask the old man about this kind of thing, his immediate response is "Spray the whole thing down with Ortheen". Would that or any other tree/shrub protectant be useful, or do you just let it run its course?

I'd let it run its course. Spraying won't help, and would probably hinder as it would prevent the natural control predatory insects from catching up with the midges.

Resin

Most galls do not adversely affect plant health. Therefore, gall control is generally not recommended. However you can prune galls out when you first discover them if it not very bad. Chemical applications are an option, but are often ineffective since the required precise timing of sprays is difficult. To be effective, sprays must be timed to coincide with initial insect/mite activity before gall formation begins. Once galls start to form, they conceal the causal organism and control is very difficult. The only treatment that could be recommended for this insect is application of an insecticide during new leaf emergence in spring. Orthene, as a systemic insecticide can be applied to the foliage, and might be a pretty good choice.