I organize my kits by designer. If I buy them from a store that has several designers (such as DD), I make a folder for that store, and then create individual folders for each designer in that folder. I tend to remember kits and styles by "designer" so that works for me. But you have to find whatever organizational method best works for you.
No matter how well the kits are organized though, I am finding that I have amassing one *mammoth* collection, and over time I forget I even have certain things! I've seriously considered printing out all of the preview files and keeping them in a binder so I can quickly peruse what I have before digging into a layout.
