Here's what I've done:
Years 1-2, just remembered
Years 3-8, kept programs saved in the same folder so I could go back and look.
Sporadically, written it down on the folder
Every so often, made cryptic notes in Charms that I later don't understand.
I'm spending some time this summer trying to get much more advanced with Excel (getting ready to break up with Charms), so I'm open to keeping track there. If you do, what's the syntax? What specifically do you input?