I have been using spaced repetition for the last 11 years to remember things, and I totally love it. I don't really like reading books, I prefer to listen to them. My solution for not being able to make flashcards while I'm reading a book is to listen to the audio book, when I hear a passage that I want to recall or think about, I write it down in a note taking app on my phone (I just use the default Notes app on my iphone), and then review my notes every couple of days and make flashcards of the stuff contained in notes.
There is too much blowback and ignorance in regards to how memory and thinking works. We have been horribly brainwashed into thinking that all memorization is bad and that focusing on "critical thinking skills" is superior. In order to think any thought, memory is required. Rather than memorizing useless facts, schools should use spaced repetition from the first grade onwards to ensure long term retention over important ideas and concepts. This needs to be implemented on every level of our education system. Far too much ignorance and bureaucracy stands in the way of this ever happening, but at least those tools are in the hands of any autodidact that wants to use it.
I have used SuperMemo for the last nine years of my life to learn three languages, lots of scientific concepts I had long forgotten after leaving school, world history, jokes and countless other information. Spaced repetition is one of the coolest modern inventions and one of the best uses of computers on the human mind that I know of. It totally rocks as long as you put in effort.