I use the noguchi filing system (http://www.lise.jp/noguchi.html). Basically, it's just an LRU for documents. No categories, no filtering, just insert everything on the left side (whether it's new or something you just accessed).

I think any filing system you use needs to have O(1) no thought required inserts because inserts are so much more common than reads. I'm willing to tolerate a bit of time looking for what I need (though I can usually find everything fairly quickly) since I only do it a few times a year.