Have you noticed as you pore over your files that you can date your genealogical research by the type of paper your copies are on? As I have been going over my Wallis files, or any other files, I can always tell how old the research is by the paper. Remember when photocopy paper was slick and shiny? That converted first to real paper, but paper for microfilm copies remained slick for several years thereafter.
A more well-organized person might have dated each piece of paper. Not me. I was good in always copying the title page, but never noting the date on which I did the actual research. Whether that has served me or not is questionable. I'm sure there are times when I've re-looked at the same source for the same names. It may be a waste of time, or not. Sometimes you don't realize that you've acquired another piece of the puzzle so when you do look at a source already consulted a new name pops out at you which made no sense the first time around. Of course original research such as censuses, deeds, probates, etc. I always wrote on the back the citation. No really.
Randy Seaver has pointed to Elyse Doerflinger's blog about Organizing the Paper Mountain (in two parts). I wasn't terribly concerned because in my own way the paper mountain is organized. It sits neatly in two very large 4 drawer file cabinets, in folders properly labeled by family name. Now within the folders, it is a hodgepodge of information, in no specific order. But it is organized! I can generally find what I want within minutes, and that's my gauge to organization of any kind. Transforming the paper mountain into a digital molehill is a different matter. I've yet to attempt such a thing (but ought to).