Online poker sites make it really easy to take notes on players. some sites like Full Tilt Poker let you color code notes, which can makes it easy to categorize poker players based on their playing style. Note taking is a feature that should not be ignored.
Taking notes on poker players will come in handy most at higher limits, because you’ll run into the same players more often, but it helps a lot at lower limits as well.
If you notice someone playing tight and passive, make a note that they’re a TAP player. Loose and agressive players should be noted as LAGs, and so on.
If you see a player folding to a check raise every time, make a note of it. Next time you’re involved in a hand with him, you can use this to your advantage.
The edge one player has over another in poker is very slim, so you have to take every advantage you can get to maximize your edge. Keeping notes on players and categorizing them based on their playing style is a very valuable skill.
Just want to add, that when taking notes that it important that you use some form of shorthand that you can quickly type in. And of course you want to be able to understand what the shorthand means when you read it again several months after taking the notes.
I don’t want to suggest a list of abbreviations. It is essential that you think of your own abbreviations and shorthand.
But as an example, one of mine is OBORWS. This means On button, only raises with strength. It gives me a fairly good indication of how that person plays when on the button, and also lets me know how to defend my blinds against him.