I'd write it down in a text file. Much easier to keep, find, backup, and I don't lose it like I'd lose a paper. My biggest project had about 3MB of text files, one of them a 25 page document explaining to me what all the formulas were for. Quite impressive, I even used it for college applications. I think I'll get back to work on it next year, along with upgrading the Click FAQ
Imagine the mess if all those pages on paper
Disclaimer: Any sarcasm in my posts will not be mentioned as that would ruin the purpose. It is assumed that the reader is intelligent enough to tell the difference between what is sarcasm and what is not.