Notes will absolutely help if you play with the same person quite a bit. You'll get a ton of info over a large number of hands, and they aren't going to change their play too too much. However, if you only have a very small sample size of hands, and you don't play someone often at all (As is often the case in the micros), they are of course going to be less helpful.
Still, important to keep notes in a short session with a player...if for nothing more than it keeps your head in the game, and it might give you an advantage in a certain key situation that you wouldn't have otherwise.