[azasadny]

Joe,
I think it's the dust and carpet fibers that get pulled into the PC when the carpets are vacuumed and pets (at home, not the office). We used to have a pet rabbit in the basement, where my PC is and it used to get rabbit fur all over the inside of the case, especially if the tower sits on the floor, which most of them do. Glad I was able to help by reminding people to clean up their PC's!