I don't take notes during a session. I watch the players and remember what they do in the current game. If I have been playing with the same player consistently, I will take notes on her away from the table.

In terms of results, I only track my hourly rate. You could use that to estimate your BB/100 if you wanted, but it wouldn't be as accurate as online. I wouldn't bother keeping track of other details.

Something else you may want to take notes on is yourself.