Just a recommendation on the use of "Scotchbrite" or other scrubbing materials:
If you can find it, get the white stuff rather than the green, grey or maroon (or whatever other color you find). The white has no abrasive in it, the others all do. While its quite well bonded to the fibers, the abrasive can only do harm if it gets into things like fan bearings, etc.
I recommend a hardware store to find the white.
What I use for intake filters is 3M's "Filtrete" material (for window air conditioners) spread over a piece of aluminum expanded metal. I was able to fit this under the plastic front cover of both my Antec cases. I "dome" the expanded metal as much as possible to increase the surface area and stil seal off on the edges. The expanded metal is just a piece of "rain gutter screen", again available at many hardware stores.
With any filter system, the key is to have as much filter surface area as possible. That reduces the flow resistance, and also allows a larger surface area to collect the dust so cleaning/changing filters is reduced (but not eliminated). The problem with filters that go directly over the fan is that they have a small surface area so are restrictive even when clean, and get dirty and thus more restrictive very quickly.
my $.02
BW