I have just begun compiling my opening repertoire into a tangible form which will allow me to review and study my particular lines. I guess in today's world note cards are a thing of the past.
Several different options of software are available and various methods to approach this monumental task but the results will be well worth it. Once entered, being able to search and update your opening lines with just a few clicks will be worth its weight in gold.
Currently Steve Lopez the "How To Guru Extraordinaire" of Chess Base fame is running articles on his approach to creating such a study book. Really cool read if you have the time.
Since this post is starting to run long I will have to continue this a bit later.