i actually do things pretty similar to joanne. the preview folder was the best thing i ever did for my kits...it really does make finding things much easier.
as for my commercial use stuff...i have one main folder called CU Supplies...then within it, several sub folders for BOWS, FRAMES, OVERLAYS, etc. then when i get something new, if it isn't named by the designer, i name it and put it in the folder it belongs. so for example, say i have a set of bows, i would name all the files TwinMomScraps. then each time i add more bows with the same name, all my bows will eventually be names like this: TwinMomScraps(1), TwinMomScraps(2), TwinMomScraps(3), etc...and the numbering is automatically done by my computer. sooooo....all my TwinMomScraps stuff is together, and each of the other designers' stuff is all together too.
hope that made sense...LOL!
i also move all my old stuff to my external hard drive every month or so. the only stuff i keep on my laptop long term is my CU folder, and whatever i am currently working on for the month. i should burn to disc though as mentioned above though...just never got around to it