Great topic.
I'm getting back into hobbyist electronics after years of software-only life, and I need something to refresh the stuff I learned at the university, and to augment it with practical knowledge in areas we never covered (such as audio)...
My question would be, what is a good source of practical knowledge? I spent long painful nights over Maxwell equations, Laplace transformations and transfer functions, but I am thoroughly lacking in practical stuff that got built up over years and years of engineering history - like sizing filter capacitors, when to use them, when to go with a Zener diode and when with an ohmic voltage divider, practical ways of helping an op-amp give its best, etc.