Ive just been jotting notes on my recipe sheet from Norther Brewer, however when I start all grain, I planned on printing out the recipe from Beer Smith and then writing on them instead. Ive been laminating those recipe sheets after bottling and then putting them in a big binder i have with alot of different sheets of info from yeast starters, to keg pressures to IBU ratings for hops, BJCP ratings for beer styles, etc. I like having a binder with laminated sheets better then just a notepad as i can a bit messy when brewing.
Other then just jotting down notes, I think the next most important thing is keeping them all in the same place where u can easy look back to previous batches and notes in case u want to try something that worked before. Everything will be readily available at your fingertips, u don't have to worry about stepping away from a boiling kettle of wort or an autosiphon or anything like that.