Back in August I mentioned that we were going to give a modified workbox method a try, and we've been doing just that rather happily since then. We dont' use the boxes as a guide for our days, though, we use our days as a guide for the boxes.
We have a stack of six craft-box drawers that started out in our play room but have since migrated to our kitchen, and we keep them filled with things that are on the top of Calvin's interest list at the moment. We ended up labeling the boxes with seven different basic subjects for organizing purposes. Right now there's mammoths and kingdom classification (BFSU) in the science drawer, map mystery worksheets in the geography drawer, subtraction from Math-U-See in the math drawer, some Dover coloring books and his piano books in the art and music drawer, and his journal is in the language drawer.
We have no rules about how or when things get done, or about what can or can't go in the boxes, we use them instead as suggestions in moments of mid-day ennui ("what do we do now?" "I don't know, why don't we take a look in the boxes?"), and we tend to visit at least one box every day, some days all six. They give Calvin a place to keep projects that are in the works, and they are great for keeping our minds focused, so that we don't forget projects that are in the works or questions that we haven't been able to fully answer just yet. And as I find interesting books, print-outs, etc., I put them in the appropriate drawer for the boy to find on a rainy day.
As a means of organization the boxes have been great, and using them this way they fit right into my dreams and aspirations for an unschooling environment.