I believe note systems are great! The only problem, and I see people talking too little about it, is that you need to create your own, for it to be effective.

It's like trying to use spaced repetition with cards made by someone else, you loose 80% of the benefit.

Creating, perfecting (and using) your own note system is what makes you a learning machine, as it let's you understand how your mind process and learn information. Your system is a reflex of your own mind, and exposes (reasonably) to you how the inner words.

Very hard, thought, as you need a very high level of meta thought. Hence a lot of people see someone's else system and try to use it, benefit poorly from it.

You can and should learn from other's systems, but to perfect what you made yourself.