When I first started martial arts, in TKD and Kali (two different schools), I kept copious notes on every detail. Then about 2-3 years in, I stopped taking as profuse notes, as I figured I would just "absorb" the lessons and eventually hit the same material again.
However, recently (last year or so), I have started keeping a notebook again. I have a spiralbound (actually, a couple but I just use which happens to be closest), and then I transfer (sometimes) my notes to the computer. I also kept a log of my workouts. However, my computer has recently died, so I have been reduced to keeping notes in my notebooks.
I used to get really frustrated if I missed something in my notebook, but now I use it much more casually. If i think of something neat, I write it down. If I forget to write down something, I don't make such a big deal as I used to. However, I try to get the proper terminology down.
Bryan