This is excellent advice, jdubb!
No matter what you use for taking notes (paper, Word, OneNote, BeerSmith, crayons, etc.) it is IMPERATIVE you capture the salient points of the brew day. Write down the good, bad and the ugly because you won't remember the fine details later on. And, like jdubb said, what you might assume is a mistake or blunder can turn out to be gold.
The best $20 I ever spent on anything related to beer was BeerSmith. I use it to manage my recipes and it's fantastic. I use MSFT OneNote for my notes (BeerSmith has a small section and it just isn't enough space, IMHO).
Brew on!