I use a fair bit of my schooling. Instrumentation comes in handy for the vibration monitoring side of my job. PLCs was a good elective, I know enough to tell when things are really screwed up. I actually use a fair bit of basic vector math when doing 2 plane static couple balancing of over hung fans, same with Vibs. Various machine design classes are useful day to day. Other electives such as facilities planning and project management have been an asset at various times. Most of my core text books sit on my shelf at work and are fairly well covered in greasy taconite dust finger prints. I would say my most useless classes were in the humanities department, with the exception being German 1&2. I understand the purpose a liberal arts education but I honestly believe for myself personally I would have been better off with crash course in mine engineering than taking world cultures and institutions, a lot of that material was rehashed 10th grade US history, 11th grade world history & 12th grade civics. The elective I would most recommend is USAF ROTC Basic Leadership. One year it was opened up to non cadets, I learned more in they class then 3 humanities classes that covered the same material. Both of those class manuals sit on my shelf and get used at least once a month.