Yes, I keep notes but am trying to learn to make them more useful than in the past. But, I don't make every single decision based on a few notes. I mostly play tourneys, so there are some players that I see over and over, but many that are just once in a while - so you can't be certain of the latter as there is little data. However, the ones I see more regularly are more helpful, of course the better players mix it up anyway, so you still have to pay attention to other aspects as well.