saton472: I do have filters on all my intake fans - if you read the text of the first post you would see I was cleaning them when I found that stain on the block. You don't wanna see the fist-size pile'o'dust I pulled out of the filters before I took those pics
(actually - mostly dog-hair - any other dog-owners here should be able to confirm that pets do tend to fill computers with unwanted fur/dust)