Going freelance. All the stuff I learned in formal and informal study and from those around me pales in comparison to what I learned from having to craft useful, affordable solutions for a wide variety of customers in several different fields.

It's true that certain aspects of my technical knowledge took a hit, but creating line of business software solutions in direct collaboration with the actual end-users was a transformative experience.

One of the most important things I learned is that approximately nobody actually knows much about how to efficiently and effectively use a computer. About one third of my time was spent teaching people how to use computers.