I recently started reading "Clean Code" by "Uncle Bob" Martin and I've decided to incorporate adding notecards on what I've come across. I've created a few cards already.

But in terms of making cards on books I read for pleasure, I agree in that it seems like overkill. One of my favorite biographies is "Peter the Great" by Robert Massie, and as much as I love reading it attempting to memorize names and details and jam pack my brain with facts would fry my brain.